Vortex generator structure suitable for axial flow fan

Abstract

The invention provides a vortex generator structure suitable for an axial flow fan, and belongs to the technical field of axial flow fans, the vortex generator structure comprises multiple groups of vortex generators circumferentially and uniformly arranged on the inner circumferential surface of a shell, and the vortex generators are located on the sides, facing an air inlet, of blades and are close to the blades; each group of vortex generators comprises two fins which are arranged in a relatively inclined manner, the sides, facing the air inlet, of the two fins are close to each other, and the sides, deviating from the air inlet, of the two fins are far away from each other; each fin comprises a connecting outer edge, a curve inner edge and a base, the base is connected between the shell and the connecting outer edge, the curve inner edge is connected to the inner side, facing the axis of the shell, of the connecting outer edge, and the inner side, facing the axis of the shell, of the curve inner edge is in a curve shape. According to the invention, the fins with certain angles are arranged on the outer wall of the fan close to the blade tops, so that a plurality of groups of high-energy vortexes are generated when airflow passes through the fins, the flow separation at the blade tops can be effectively controlled, and the stall of the blades is delayed or inhibited.

Description

Technical Field

[0001] The present invention belongs to the technical field of axial flow fans, and more particularly, relates to a vortex generator structure suitable for axial flow fans. Background Art

[0002] Axial-flow fans are among the most critical axial-flow machines in power plants. With the increasing demand for tight regulation of peak performance in thermal power units, rotating machinery can exhibit instabilities during rapid load fluctuations when there is a discrepancy between fan pressure and flow. When the flow velocity drops below a critical threshold, the flow field within the fan transitions from stable to unstable, inducing rotating stall. Rotating stall in rotating machinery can be caused by a variety of factors, leading to stress fluctuations that exacerbate flow field turbulence, shorten rotor blade life, and disrupt normal fan operation.

[0003] During wind turbine blade operation, flow separation is prone to occur as air passes through the blades, a phenomenon that is particularly pronounced at high wind speeds. Flow separation occurs when airflow separates from the airfoil surface due to the adverse pressure gradient, forming a wake region of considerable thickness. This wake region results in significant kinetic energy loss and a large pressure differential, which in turn degrades the blade's aerodynamic performance. When flow separation occurs on the blade surface, it reduces the blade's stall angle of attack, lowering the maximum lift coefficient while also increasing the blade's drag. When separation reaches a certain level, the blade stalls, significantly reducing airflow capacity. Analysis of the impeller's internal flow field during the onset and development stages of stall reveals that the stall cluster originates at the blade tip. As the stall cluster propagates, a small area of ​​backflow occurs in the impeller flow channel along the propagation direction. This backflow then gradually increases in scope and intensity, completely blocking the flow channel. Eventually, the backflow caused by the stall cluster rapidly weakens, the flow channel escapes the stall, and normal flow returns to normal.

[0004] To address the aforementioned technical issues, a widely used technology is to install vortex generators (VGs) on the blade surface. A VG is a device that generates vortices in an airflow. Its principle is to utilize the relative motion between the airflow and the VG to form a set of high-energy wingtip vortices at the wingtip of the VG. These wingtip vortices mix with the low-energy boundary layer flow downstream of the airfoil, transferring energy to the boundary layer. This allows the boundary layer airflow in the adverse pressure gradient to continue adhering to the airfoil surface after gaining energy, thereby suppressing or delaying the occurrence of flow separation and improving the aerodynamic performance of the blade. Parameters such as the shape, size, position, number, and direction of the VG will affect the intensity, distribution, and duration of the vortices it generates, and thus its ability to control flow separation.

[0005] The existing vortex generator (VG) is mostly in the form of a blade, such as a rectangle, a triangle or a trapezoid. When installed, the vortex generator is basically perpendicular to the surface of the blade and the leading edge of the blade. The vortex generator is arranged in pairs, each pair of vortex generators is arranged in the shape of an "eight", and the vortex generator forms a certain angle with the incoming flow direction. The vortex generator has the advantages of simple structure, easy installation and the ability to improve the aerodynamic performance of the blade to a certain extent, but also has some disadvantages and deficiencies.

[0006] The existing VG is a simple sheet structure, each VG generates a group of wing tip vortices, and the high and low energy exchange is limited. The efficiency of low energy fluid transfer needs to be further improved to effectively delay the flow separation on the surface of the blade, so as to improve the lift of the blade and increase the output power of the unit. Therefore, the existing VG has limited ability to improve the efficiency of low energy fluid transfer and effectively delay the flow separation on the surface of the blade, thereby limiting the potential of the VG in improving the lift of the fan blade and increasing the output power of the unit. SUMMARY

[0007] The purpose of the present application is to provide a vortex generator structure suitable for an axial flow fan to solve the technical problem that the existing VG has limited ability to improve the efficiency of low energy fluid transfer and effectively delay the flow separation on the surface of the blade in the prior art.

[0008] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is to provide a vortex generator structure suitable for an axial flow fan, the axial flow fan comprising a circular ring-shaped shell and a blade located inside the shell; the vortex generator structure comprises a plurality of groups of vortex generators uniformly arranged on the inner circumferential surface of the shell, the vortex generators are located on the side of the blade facing the air inlet and close to the blade; each group of vortex generators comprises two oppositely inclined fins, the side of the two fins facing the air inlet is close to each other, and the side of the two fins away from the air inlet is away from each other; the fin comprises a connecting outer edge, a curved inner edge and a base, the base is connected between the shell and the connecting outer edge, the curved inner edge is connected to the inner side of the connecting outer edge facing the axis of the shell, and the inner side of the curved inner edge facing the axis of the shell is curved.

[0009] In combination with the above technical scheme, in a possible implementation manner, the included angle of each fin with respect to the axis direction of the shell ranges from 10° to 40°.

[0010] In combination with the above technical scheme, in a possible implementation manner, the length of the entire vortex generator ranges from 4cm to 8cm, the width ranges from 2cm to 4cm, and the height of the vortex generator is 40% to 80% of the length.

[0011] With the above technical solution, in a possible implementation, the base is arranged at two ends of the connecting outer edge on the side facing the shell.

[0012] With the above technical solution, in a possible implementation, the base is welded by cutting waste of the connecting outer edge and the curved inner edge.

[0013] With the above technical solution, in a possible implementation, the base is bent from the side of the connecting outer edge close to the shell.

[0014] With the above technical solution, in a possible implementation, the base is arranged in sealing with the inner circumferential surface of the shell.

[0015] With the above technical solution, in a possible implementation, the curved inner edge comprises at least two hump curve sections connected with each other.

[0016] With the above technical solution, in a possible implementation, a bent plate is arranged on the side of the connecting of the connecting outer edge and the curved inner edge.

[0017] With the above technical solution, in a possible implementation, the base is fixed on the inner circumferential surface of the shell by glue or double-sided tape.

[0018] The vortex generator structure suitable for the axial flow fan has the advantages that, compared with the prior art, the vortex generator structure of the application can effectively control the flow separation at the blade top position, delay or inhibit the stall of the blade, by installing fins with a certain angle on the outer wall of the fan close to the blade top position, so that a plurality of high-energy vortexes are generated when the airflow passes through the fins; the vortex generator generates induced vortexes in the corner area of the blade top, so that the low-energy fluid in the corner area is fully mixed with the main flow, thereby inhibiting the aggregation of the low-energy fluid in the corner area, controlling the influence range of the separation in the corner area on the suction surface of the blade, reducing the flow loss, improving the load of the blade near the blade root, without the need of additional energy or driving device, without affecting the structural strength and durability of the fan blade, and with good engineering practicability and economy. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the application, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor.

[0020] Figure 1A schematic diagram of the installation of a vortex generator structure suitable for an axial flow fan provided in an embodiment of the present invention;

[0021] Figure 2 Schematic diagram of the structure of the vortex generator provided in the embodiment of the present invention Figure 1 ;

[0022] Figure 3 Schematic diagram of the structure of the vortex generator provided in the embodiment of the present invention Figure 2 ;

[0023] Figure 4 Schematic diagram of the structure of the vortex generator provided in the embodiment of the present invention Figure 3 ;

[0024] Figure 5 Schematic diagram of the structure of the vortex generator provided in the embodiment of the present invention Figure 4 ;

[0025] Figure 6 Schematic diagram of the structure of the vortex generator provided in the embodiment of the present invention Figure 5 ;

[0026] Figure 7 Schematic diagram of the structure of the vortex generator provided in the embodiment of the present invention Figure 6 .

[0027] Among them, the reference numerals in the figures are as follows:

[0028] 1. Shell; 2. Vortex generator; 21. Fin; 211. Connecting outer edge; 212. Curved inner edge; 213. Base; 3. Hump curve portion; 4. Bent plate. DETAILED DESCRIPTION

[0029] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer, the present invention is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the described embodiments are only part of the embodiments of this application, rather than all the embodiments, and the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0030] It should be further explained that the drawings and implementation methods of the present invention mainly describe the concept of the present invention. Based on this concept, the specific forms and settings of some connection relationships and positional relationships may not be fully described. However, on the premise that those skilled in the art understand the concept of the present invention, those skilled in the art can implement the above-mentioned specific forms and settings in a familiar manner.

[0031] When an element is referred to as being "on" or "connected to" another element, it can be directly on or connected to the other element or indirectly on or connected to the other element by way of one or more other elements.

[0032] The terms "inner", "outer", "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "in", "out" and the like, merely indicate or suggest directions or positions in the description of the present application and do not indicate or imply absolute directions or positions of devices or elements in use or operation.

[0033] For the purpose of the description, spatially relative terms, such as "above", "below", "top", "bottom", "up", "down", "side", "horizontal", "vertical", "front", "rear", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "in", "out", and the like, are used to describe the spatial relationship of one device or feature to another device or feature as shown in the drawings. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientations depicted in the figures. For example, if a device is inverted in the figures, a device described as "above" or "above" other devices or features would be positioned "below" or "below" other devices or features. Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways, and the spatially relative descriptions used herein are interpreted accordingly. The terms "first", "second", "third", etc., are used only to describe different features and do not indicate or imply relative importance or a specific number of features. Thus, a feature defined with "first", "second", etc. can explicitly or implicitly include one or more such features. In the description of the present application, "multiple" means two or more, and "several" means one or more, unless otherwise explicitly specified.

[0034] The terms "first", "second", "third", etc. are used only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined with "first", "second", etc. can explicitly or implicitly include one or more such features. In the description of the present application, "multiple" means two or more, and "several" means one or more, unless otherwise explicitly specified.

[0035] Now a vortex generator structure suitable for axial flow fan is described.

[0036] As Figure 1 and Figure 2As shown, an embodiment of the present invention provides a vortex generator 2 structure suitable for an axial flow fan, the axial flow fan includes a ring-shaped shell 1 and blades located inside the shell 1; the vortex generator 2 structure includes a plurality of groups of vortex generators 2 that are evenly arranged on the inner circumference of the shell 1, and the vortex generators 2 are located on the side of the blade facing the air inlet and close to the blade; each group of vortex generators 2 includes two fins 21 that are relatively inclined, the two fins 21 are close to each other on the side facing the air inlet, and the two fins 21 are far away from each other on the side away from the air inlet; the fin 21 includes a connecting outer edge 211, a curved inner edge 212 and a base 213, the base 213 is connected between the shell 1 and the connecting outer edge 211, the curved inner edge 212 is connected to the inner side of the connecting outer edge 211 facing the axis of the shell 1, and the curved inner edge 212 is curved on the inner side of the axis of the shell 1.

[0037] Furthermore, the blades of the axial flow fan are divided into moving blades and stationary blades. The moving blades are located on the side close to the air inlet, and the stationary blades are located on the side close to the air outlet. The vortex generator 2 is located on the side of the moving blades facing the air inlet.

[0038] Specifically, the longitudinal direction of an axial fan corresponds to the direction of air intake, i.e., the direction of air flow directed toward vortex generator 2 during normal operation. Vortex generator 2 is fixed to the inner surface of the fan's outer wall, so the longitudinal direction corresponds to the axial direction of the fan blades. For fins 21, the outer edge indicates the direction toward the inside of housing 1, while the inner edge indicates the direction toward the inside of housing 1.

[0039] Specifically, the two fins 21 in each group of vortex generators 2 are arranged in mirror symmetry.

[0040] The present embodiment provides a vortex generator 2 structure suitable for an axial flow fan. Compared with the prior art, by installing fins 21 at a certain angle on the outer wall of the fan near the blade tip, multiple groups of high-energy vortices are generated when the airflow passes through the fins 21, which can effectively control the flow separation at the blade tip position and delay or suppress the stall of the blade; taking advantage of the fact that the airflow velocity at the blade tip part is higher when the axial flow fan is intake, the vortex generator 2 generates an induced vortex in the blade tip corner area, so that the low-energy fluid in the corner area is fully mixed with the mainstream, thereby suppressing the aggregation of the low-energy fluid in the corner area, controlling the influence range of the corner area separation on the suction surface of the blade, reducing flow losses, and increasing the blade load near the blade root. It does not require additional energy or driving device, will not affect the structural strength and durability of the fan blade, and has good engineering practicality and economy.

[0041] like Figures 2 to 3 As shown, the present invention provides a specific implementation method based on the above implementation method as follows:

[0042] The angle of each fin 21 relative to the axis of the housing 1 is in the range of 10°-40°.

[0043] That is, the two fins 21 are aligned relative to each other within a range of 20° to 80°, which increases the applicability of the vortex generator 2 .

[0044] like Figures 2 to 3 As shown, the present invention provides a specific implementation method based on the above implementation method as follows:

[0045] The length of the entire vortex generator 2 is in the range of 4 cm to 8 cm, the width is in the range of 2 cm to 4 cm, and the height of the vortex generator 2 is 40% to 80% of its length.

[0046] Specifically, the entire vortex generator 2 can be made of a relatively hard, non-bending material, such as hard metal. Fiber composite materials are an alternative material. The vortex generator 2 can be integrally formed or composed of multiple components.

[0047] like Figure 2 As shown, the present invention provides a specific implementation method based on the above implementation method as follows:

[0048] The base 213 is provided at both ends of the connecting outer edge 211 facing the housing 1 .

[0049] The base 213 is connected between the two ends of the connecting outer edge 211 and the inner circumferential surface of the shell 1 , and can improve the connection stability between the connecting outer edge 211 and the shell 1 .

[0050] like Figure 2 As shown, the present invention provides a specific implementation method based on the above implementation method as follows:

[0051] The base 213 is formed by welding the cut scraps connecting the outer edge 211 and the curved inner edge 212 .

[0052] It is convenient to use local materials, more environmentally friendly and reduces costs.

[0053] like Figure 3 As shown, the present invention provides a specific implementation method based on the above implementation method as follows:

[0054] The base 213 is formed by bending a side of the connecting outer edge 211 close to the housing 1 .

[0055] Bending allows for a high degree of dimensional stability and simple production steps.

[0056] Furthermore, in this embodiment, the vortex generator 2 is made of a flat plate material, specifically aluminum or stainless steel.

[0057] like Figures 2 to 3 As shown, the present invention provides a specific implementation method based on the above implementation method as follows:

[0058] The base 213 and the inner peripheral surface of the housing 1 are sealed.

[0059] Specifically, sealing can be achieved using a sealant, such as a silicone material. This sealant can be installed around the inner circumference of the housing 1 or between the connecting outer edge 211 of the fin 21 and the inner circumference of the housing 1. This seal protects the bond from external influences and prevents the accumulation of contaminants. Furthermore, sealing can achieve a more optimal aerodynamic shape.

[0060] like Figures 4 and 5 As shown, the present invention provides a specific implementation method based on the above implementation method as follows:

[0061] A bent plate 4 is provided on one side of the connection between the outer edge 211 and the curved inner edge 212 .

[0062] The provision of the bent plate 4 can, on the one hand, enhance the rigidity of the fin 21 , and on the other hand, improve the anti-vibration capability of the fin 21 .

[0063] like Figures 6 and 7 As shown, the present invention provides a specific implementation method based on the above implementation method as follows:

[0064] The curved inner edge 212 includes at least two camel-hump curve portions 3 connected to each other.

[0065] Specifically, in this embodiment, there are two hump curve portions 3. Changing the single convex curve to a double convex curve can adjust the vortex intensity and frequency of the vortex generator 2, thereby adapting to different wind speed conditions and achieving active flow control of the axial flow fan blades.

[0066] like Figures 1 to 2 As shown, the present invention provides a specific implementation method based on the above implementation method as follows:

[0067] The base 213 is fixed to the inner circumference of the housing 1 by glue or double-sided tape.

[0068] Specifically, in this embodiment, double-sided tape is used to adhere the base 213 to the inner circumferential surface of the housing 1. The tape can have an elastic layer, particularly made of a foam material, and can be 1 mm thick or more. This allows for bridging differences in gap sizes. The vortex generator 2 can be simply adhered to the inner surface of the axial fan's outer wall without requiring any additional pre-treatment.

[0069] refer to Figure 2In some possible embodiments, the curved inner edge 212 is a single convex curve, the base 213 is welded at both ends of the connecting outer edge 211, no seal is arranged between the connecting outer edge 211 and the inner circumferential surface of the shell 1, and no bending plate 4 is arranged between the connecting outer edge 211 and the curved inner edge 212.

[0070] With reference to Figure 3 In some possible embodiments, the curved inner edge 212 is a single convex curve, the base 213 is bent from the connecting outer edge 211, a seal is arranged between the connecting outer edge 211 and the inner circumferential surface of the shell 1, and no bending plate 4 is arranged between the connecting outer edge 211 and the curved inner edge 212.

[0071] With reference to Figure 4 In some possible embodiments, the curved inner edge 212 is a single convex curve, the base 213 is welded at both ends of the connecting outer edge 211, no seal is arranged between the connecting outer edge 211 and the inner circumferential surface of the shell 1, and a bending plate 4 is arranged between the connecting outer edge 211 and the curved inner edge 212.

[0072] With reference to Figure 5 In some possible embodiments, the curved inner edge 212 is a single convex curve, the base 213 is bent from the connecting outer edge 211, a seal is arranged between the connecting outer edge 211 and the inner circumferential surface of the shell 1, and a bending plate 4 is arranged between the connecting outer edge 211 and the curved inner edge 212.

[0073] With reference to Figure 6 In some possible embodiments, the curved inner edge 212 is a double hump curve part 3, the base 213 is bent from the connecting outer edge 211, a seal is arranged between the connecting outer edge 211 and the inner circumferential surface of the shell 1, and no bending plate 4 is arranged between the connecting outer edge 211 and the curved inner edge 212.

[0074] With reference to Figure 7 In some possible embodiments, the curved inner edge 212 is a single convex curve, the base 213 is welded at both ends of the connecting outer edge 211, no seal is arranged between the connecting outer edge 211 and the inner circumferential surface of the shell 1, and no bending plate 4 is arranged between the connecting outer edge 211 and the curved inner edge 212.

[0075] In summary, the application can effectively generate and maintain stable vortex flow on the tip region of the blade of the axial flow fan by arranging a plurality of vortex generators 2 on the inner circumferential surface of the shell 1 of the axial flow fan, arranging two fins 21 in each vortex generator 2 in a “eight”-shaped line symmetrically to form a bifurcated structure, effectively delaying the flow separation on the surface of the blade, and achieving the purpose of increasing the lift of the blade and the output power.

[0076] The present invention optimizes the generation of vortices and the control of airflow by setting parameters such as the length, width, shape and angle of the fins 21, and can adjust the vortex intensity and frequency of the vortex generator 2 to adapt to different wind speed conditions, thereby achieving active flow control of the axial flow fan blades and improving the stability and reliability of the fan.

[0077] Compared with the conventional vortex generator 2 fixed on the blade, the vortex generator 2 of the present invention has a simple structure, low production cost, easy installation, does not require additional energy or drive device, is compatible with the structure and material of the outer wall, does not affect the structural strength and durability of the fan blade, and does not increase the weight and resistance of the fan blade itself, and has good engineering practicality and economy.

[0078] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

[0079] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0080] Unless otherwise specified, the relative arrangement of the parts and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present application. Meanwhile, it should be understood that, for ease of description, the sizes of the various parts shown in the accompanying drawings are not drawn according to actual proportional relationships. Technology, methods and equipment known to those of ordinary skill in the relevant art may not be discussed in detail, but in appropriate cases, the technology, methods and equipment should be considered as a part of the specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments can have different values. It should be noted that similar numbers and letters represent similar items in the following drawings, and therefore, once an item is defined in an accompanying drawing, it does not need to be further discussed in subsequent drawings.

Claims

1. A vortex generator structure suitable for an axial flow fan, characterized in that: The axial flow fan comprises a circular shell (1) and blades located inside the shell (1); the vortex generator (2) structure comprises a plurality of groups of vortex generators (2) uniformly arranged on the inner circumference of the shell (1), the vortex generators (2) being located on the side of the blades facing the air inlet and close to the blades; each group of the vortex generators (2) comprises two fins (21) arranged relatively obliquely, the two fins (21) being close to each other on the side facing the air inlet, and the two fins (21) being close to each other on the side facing the air inlet. The fins (21) are spaced apart from each other on the side facing away from the air inlet; the fins (21) include a connecting outer edge (211), a curved inner edge (212) and a base (213); the base (213) is connected between the shell (1) and the connecting outer edge (211); the curved inner edge (212) is connected to the inner side of the connecting outer edge (211) toward the axis of the shell (1); and the curved inner edge (212) is curved toward the inner side of the axis of the shell (1).

2. A vortex generator structure suitable for an axial flow fan according to claim 1, characterized in that: The angle of each fin (21) relative to the axial direction of the housing (1) ranges from 10° to 40°.

3. A vortex generator structure suitable for an axial flow fan according to claim 1, characterized in that: The length of the entire vortex generator (2) ranges from 4 cm to 8 cm, the width ranges from 2 cm to 4 cm, and the height of the vortex generator (2) ranges from 40% to 80% of its length.

4. A vortex generator structure suitable for an axial flow fan according to claim 1, characterized in that: The base (213) is arranged at both ends of the connecting outer edge (211) facing the housing (1).

5. A vortex generator structure suitable for an axial flow fan according to claim 4, characterized in that: The base (213) is formed by welding the cut waste of the connecting outer edge (211) and the curved inner edge (212).

6. A vortex generator structure suitable for an axial flow fan according to claim 1, characterized in that: The base (213) is formed by bending the connecting outer edge (211) on one side close to the shell (1).

7. A vortex generator structure suitable for an axial flow fan according to claim 6, characterized in that: The base (213) and the inner peripheral surface of the shell (1) are sealed.

8. A vortex generator structure suitable for an axial flow fan according to any one of claims 4 to 7, characterized in that: The curved inner edge (212) includes at least two mutually connected hump curve portions (3).

9. A vortex generator structure suitable for an axial flow fan according to any one of claims 4 to 7, characterized in that: A bending plate (4) is provided on one side of the connection between the connecting outer edge (211) and the curved inner edge (212).

10. A vortex generator structure suitable for an axial flow fan according to any one of claims 1 to 7, characterized in that: The base (213) is fixed to the inner circumferential surface of the shell (1) by glue or double-sided tape.

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