Axial flow fan blade gradient porosity lightweight hub structure

Abstract

The present application relates to the technical field of fan wheel hub, in particular to a gradient porosity lightweight hub structure of axial flow fan blade. The hub body includes a ring wall, and the ring wall is provided with an arc-shaped groove in the circumferential direction. The arc-shaped groove includes a mounting groove for mounting the axial flow fan blade and a noise reduction groove without mounting the axial flow fan blade. The opening of the noise reduction groove is provided with a grid-shaped connecting rib. An elastic sheet is arranged in the back cavity of the noise reduction groove. The captured vibration mechanical energy is converted into heat energy dissipation by the structural damping effect of the wave-shaped elastic sheet arranged in the back cavity of the noise reduction groove, thereby suppressing the noise from the source. At the same time, the elastic sheet is excited by the micro-jet side flow generated by the grid modulation of the connecting rib, and cooperates with the Helmholtz resonator composed of the back cavity volume and the rectangular orifice, thereby actively absorbing and canceling the specific aerodynamic noise. Thus, the wideband noise reduction and lightweight goals are achieved cooperatively under the premise of ensuring the structural strength.

Description

Technical Field

[0001] This invention relates to the field of wind turbine hub technology, and more specifically, to a lightweight hub structure with gradient porosity for axial flow wind turbines. Background Technology

[0002] When an axial flow fan is in use, the airflow direction is basically parallel to the axis of the fan's rotating shaft. An axial flow fan mainly consists of a motor, rotating shaft, impeller, and casing. The impeller itself mainly consists of a hub and blades. The basic structure of the hub includes a ring body and a bushing. The ring body is located on the outer circumference of the bushing, and the two are connected by an end plate. The bushing of the hub is used to fit onto the rotating shaft, and the ring body of the hub is used to mount the blades. Due to its simple structure, axial flow fans are widely used in household appliances such as floor fans and air purifiers.

[0003] However, when using axial fans in existing household appliances, there is an irreconcilable contradiction between lightweight design (such as adding weight-reducing holes or slots) and ensuring structural strength and suppressing operating noise in the hub of the axial fan blades. Specifically, adding weight-reducing holes or slots to traditional hubs weakens structural rigidity, making them prone to vibration and noise radiation under the action of centrifugal force during rotation; while simply increasing the material or connecting ribs to strengthen the structure can improve strength, it will increase weight and cannot effectively eliminate the vibration and aerodynamic noise already generated, making it difficult for the fan system to achieve high efficiency, lightweight design, and low noise operation. Summary of the Invention

[0004] This invention provides a lightweight hub structure with gradient porosity for axial flow fan blades. It utilizes a wave-shaped elastic sheet within the noise-reducing groove's back cavity to convert captured vibrational mechanical energy into heat dissipation through structural damping, thus suppressing noise at its source. Simultaneously, the elastic sheet is excited by a micro-jet generated by airflow modulation via connecting rib grids. This micro-jet works in conjunction with a Helmholtz resonator composed of the back cavity volume and rectangular orifices to actively absorb and cancel specific aerodynamic noise. Therefore, while ensuring structural strength, it synergistically achieves broadband noise reduction and lightweighting, thereby solving the problems mentioned in the background art.

[0005] In existing technologies, the lightweight design, structural strength improvement, and noise suppression of axial flow fan hubs are mutually restrictive and cannot be optimized simultaneously, making it difficult for fan systems to achieve high efficiency, lightweight design, and low noise operation.

[0006] To achieve the above objectives, the lightweight hub structure with gradient porosity of the axial flow fan blade includes a hub body and an axial flow fan blade. The hub body includes an annular wall, and the annular wall is provided with an arc-shaped groove in the circumferential direction.

[0007] The arc-shaped groove includes a mounting groove for installing the axial flow fan blade and a noise reduction groove where the axial flow fan blade is not installed; the opening of the noise reduction groove is provided with a grid-like connecting rib.

[0008] The noise reduction groove has a back cavity formed behind the connecting rib in the depth direction;

[0009] An elastic sheet is provided inside the back cavity, and the two ends of the elastic sheet are connected to the inner wall of the noise reduction groove through a fixing structure.

[0010] In the above technical solution, multiple noise reduction grooves are circumferentially opened on the ring wall of the wheel hub body, which achieves a significant reduction in basic weight. These noise reduction grooves, by setting grid-like connecting ribs at the openings, effectively reduce the aerodynamic opening area to reduce wind resistance and noise, while greatly enhancing the overall structural rigidity and stability of the wheel hub body and preventing the ring wall from deforming under high-speed rotation. Furthermore, elastic plates with fixed ends are cleverly set in the back cavity of each noise reduction groove. Their core function is to generate Helmholtz resonance effect or forced vibration with airflow sound waves of a specific frequency, actively absorbing and dissipating the aerodynamic noise energy of a wide frequency band, thereby achieving efficient noise reduction at the sound source.

[0011] Furthermore, the thickness of the connecting rib extending into the noise reduction groove accounts for 25%-35% of the overall depth of the noise reduction groove. The connecting rib extending to this depth of 25%-35% of the noise reduction groove forms a robust skeleton that penetrates deep into the back cavity, enhancing the ring wall's ability to resist centrifugal deformation and vibration during high-speed rotation and ensuring structural reliability. At the same time, this depth design ensures that the connecting rib has sufficient effective length to provide strong structural support, while cleverly avoiding excessive intrusion into the back cavity space, thereby maximizing the preservation of the integrity of the back cavity volume. The back cavity volume is a key parameter that determines the core noise reduction frequency of the Helmholtz resonator. Therefore, this design, while achieving excellent mechanical strength, strictly ensures the inherent frequency stability of the back cavity where the elastic sheet is located and the predictability of noise reduction performance. It is a key optimization for achieving a win-win situation of strong structure and high noise reduction.

[0012] Preferably, the elastic sheet has a wavy sheet structure. When the elastic sheet is installed in the noise reduction groove, the wavy bends of the elastic sheet contact the inner wall of the noise reduction groove. The wavy sheet structure significantly improves the broadband vibration absorption and noise reduction efficiency by introducing multi-point contact preload and structural nonlinearity. Specifically, when the elastic sheet is installed in a wavy shape, each bend forms a reliable contact point with the inner wall of the noise reduction groove. This is equivalent to providing the elastic sheet with multiple additional, distributed elastic boundary constraints, rather than simple two-end fixation. These contact points are affected by airflow. The excitation process generates slight friction and slippage, which efficiently converts the mechanical energy of vibration into heat energy for dissipation. At the same time, this pre-tightened contact state changes the stiffness and vibration mode of the elastic sheet, enabling it to excite more complex nonlinear vibrations when excited by a wide-frequency airflow, thereby broadening its effective vibration absorption frequency range and no longer being limited to a single resonant frequency. In addition, the multi-point contact support also optimizes the stress distribution on the elastic sheet, avoiding excessive local stress concentration. While significantly improving the noise reduction effect, it also ensures the fatigue strength and reliability of the elastic sheet itself under long-term high-frequency vibration.

[0013] In addition, the fixing structure includes an embedding groove formed on the inner wall of the two short sides of the noise reduction groove and a through hole that penetrates the annular wall and communicates with the embedding groove.

[0014] Furthermore, the elastic sheet is provided with fixing blocks with through holes at both ends. The fixing blocks match the embedding grooves and the elastic sheet is fixed by fasteners passing through the through holes and the through holes.

[0015] It should be added that there are multiple connecting ribs at the opening of the noise reduction groove, and the multiple connecting ribs are arranged to form a rectangular hole by interleaving each other; and the width of the connecting rib is 1-2mm, and the diameter of the rectangular hole formed between adjacent connecting ribs is 3-5mm.

[0016] In addition, the wheel hub body is made of either PBT-GF30 or PA66-GF30 engineering plastics and is integrally formed by injection molding. The noise reduction groove and the connecting rib are part of the wheel hub body.

[0017] Furthermore, the elastic sheet is made of one of 304 stainless steel, 316 stainless steel, and titanium alloy; the thickness of the elastic sheet is 0.1-0.3 mm.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] By setting a wave-shaped elastic sheet in the back cavity of the noise reduction groove, the captured vibration mechanical energy is converted into heat energy dissipation by utilizing its structural damping effect, thus suppressing noise at the source. At the same time, the elastic sheet is excited by the micro-jet generated by the airflow modulated by the connecting rib grid, and works in synergy with the Helmholtz resonator composed of the back cavity volume and rectangular orifice to actively absorb and cancel specific aerodynamic noise. Thus, while ensuring structural strength, the goals of broadband noise reduction and lightweighting are achieved in a coordinated manner. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the overall structure of the axial flow fan blade of the present invention;

[0021] Figure 2 This is a schematic diagram of the connecting rib structure after the outer side of the annular wall of the present invention is unfolded;

[0022] Figure 3 This is a schematic diagram of the unfolded elastic sheet inside the annular wall of the present invention;

[0023] Figure 4 This is a schematic diagram of the elastic sheet structure of the present invention.

[0024] The meanings of the labels in the diagram are as follows:

[0025] 100. Hub body; 101. Ring wall; 102. Arc groove; 103. Connecting rib; 104. Back cavity; 105. Elastic sheet; 106. Through hole; 107. Through hole; 108. Fixing block; 109. Mounting groove; 110. Noise reduction groove;

[0026] 200. Axial flow fan blades. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] In current technologies, the lightweight design, structural strength improvement, and noise suppression of axial flow fan hubs are mutually restrictive and cannot be optimized simultaneously. This makes it difficult for fan systems to achieve high efficiency, lightweight design, and low-noise operation. This invention provides a lightweight hub structure with gradient porosity for axial flow fan blades, such as... Figures 1-4 As shown,

[0029] The hub structure includes a hub body 100 and axial flow fan blades 200. The hub body 100 includes an annular wall 101, which is preferably 5mm thick in this design. Three sets of axial flow fan blades 200 are circumferentially mounted on the annular wall 101. The root of the axial flow fan blades is arc-shaped and matches the arc-shaped grooves 102 opened circumferentially on the annular wall 101. In this design, there are not only three sets of arc-shaped grooves 102 opened circumferentially on the annular wall 101. Between the adjacent roots of the three sets of axial flow fan blades 200, there is a separate arc-shaped groove 102 that penetrates the annular wall 101. The arc-shaped groove 102 includes a mounting groove 109 for mounting the axial flow fan blades 200 and a noise reduction groove 110 for which no axial flow fan blades 200 are mounted. The opening of the noise reduction groove 110 for which no axial flow fan blades 200 are mounted is provided with a grid-like connecting rib 103.

[0030] In the noise reduction groove 110 without the axial flow fan blade 200 installed, connecting ribs 103 are staggered on the side near the axial flow fan blade 200. The connecting ribs 103 do not completely block the noise reduction groove 110, but rather form a grid. The connecting ribs 103 extend into the noise reduction groove 110 with a thickness accounting for 30% of the overall depth of the noise reduction groove 110. This allows the hub body 100 to withstand the vibration energy caused by the rotation of the axial flow fan blade 200 while the noise reduction groove 110 is being created, preventing the centrifugal force generated by the rotation from causing structural damage to the ring wall 101. Simultaneously, the 30% thickness... The large volume of the back cavity 104 allows for a stronger Helmholtz resonance effect when wind penetrates. When the specific frequency noise generated by the fan propagates to the connecting rib 103, the resulting sound pressure drives the air to vibrate back and forth at high speed like a piston at the rectangular hole. If the noise frequency matches the inherent resonance frequency of the rectangular hole, it will generate a strong resonance, causing the air to rub violently against the wall of the connecting rib 103 in the narrow hole, thereby converting the sound energy into heat energy and consuming it. Ultimately, this achieves targeted absorption and attenuation of aerodynamic noise of a specific tone, preparing for the improvement of subsequent noise reduction performance.

[0031] The noise reduction groove 110 has two rectangular embedding grooves on its inner walls, and a through hole 106 is provided between the embedding groove and the inner side of the annular wall 101. An elastic piece 105 is provided in the back cavity 104 reserved in the noise reduction groove 110. The overall shape of the elastic piece 105 matches the noise reduction groove 110, and the elastic piece 105 is preferably wavy in this design. When the elastic piece 105 is installed in the noise reduction groove 110, the fixing blocks 108 with through holes 107 at both ends are directly embedded and matched along the rectangular embedding groove. At this time, the through holes 107 of the elastic piece 105 are coaxial with the through hole 106 of the embedding groove. Correspondingly, the operator can fix both ends of the elastic sheet 105 with small rivets or fastening screws. After fixing, each wavy bend of the elastic sheet 105 contacts the inner wall of the noise reduction groove 110. This contact method enables the axial flow fan blade 200 to transmit vibration energy from the axial flow fan blade 200 to the ring wall 101 in sequence when rotating. Since the ring wall 101 is fixedly installed with the elastic sheet 105, their rigid structure contacts each other, so that the vibration energy can be transmitted not only from the through holes 107 fixed at both ends, but also from the wavy bend of the elastic sheet 105 in contact with the inner wall of the noise reduction groove 110.

[0032] When the externally transmitted vibration frequency approaches the natural frequency of the elastic sheet 105, the elastic sheet 105 will enter a resonance state. Specifically, this resonance state is a violent oscillation that is opposite to the vibration direction of the hub body 100 and has a greater amplitude than the vibration of the hub body 100 itself. The violent oscillation of the elastic sheet 105 itself will cause the elastic sheet 105 to capture the harmful vibration mechanical energy originally concentrated on the hub body 100 and the axial flow fan blade 200 through the molecular friction inside its own material, which is equivalent to a damping effect. This energy is irreversibly converted into heat energy. Then, through the wind disturbance of the axial flow fan blade 200, the heat energy is dissipated in the air convection process. As the vibration energy is continuously consumed, the vibration, which is the root cause of noise, is suppressed, thereby reducing the operating noise of the axial flow fan blade 200.

[0033] Regarding the selection of the noise reduction groove 110, which has the same shape as the mounting root of the axial flow fan blade 200, as the mounting part for the elastic sheet 105 and the connecting rib 103 in the scheme:

[0034] Firstly, from the perspective of structural mechanics and reliability, the design of the noise reduction groove 110 is the key to achieving smooth stress transition and avoiding concentrated damage. The arc-shaped profile at the root of the axial flow fan blade 200 is the main stress path. If a rectangular groove is used, the sharp right angle of the rectangular groove will form a stress concentration point here, which will greatly increase the risk of fatigue cracks. However, by using the noise reduction groove 110, which is the same shape as the root of the axial flow fan blade 200, aerodynamic loads and centrifugal forces can be smoothly transmitted along a smooth curve. The stress flow line does not turn sharply when bypassing the groove opening, which fundamentally improves the structural integrity and fatigue life of the hub body 100 and lays the foundation for achieving a safe and reliable lightweight design.

[0035] Secondly, from the perspective of vibration control and acoustic performance, the noise reduction groove 110 ensures the matching of vibration modes and efficient energy transfer. This solution suppresses the vibration of the axial flow fan blade 200 by the forced vibration of the elastic sheet 105. The rectangular groove, due to its discontinuous stiffness distribution, will distort and hinder the transmission of vibration waves, resulting in a decrease in damping effect. The homogeneous noise reduction groove 110 and the root of the axial flow fan blade 200 form a vibration-coordinated whole, which can make the vibration waveform of the axial flow fan blade 200 more smoothly transmitted to the elastic sheet 105, greatly optimizing its reverse vibration reduction efficiency. At the same time, the smooth arc shape is also conducive to maintaining the smoothness of the aerodynamic shape and avoiding the generation of additional eddy noise.

[0036] It should be further explained that the connecting ribs 103 in the noise reduction groove 110 near the outer side of the axial flow fan blade 200 are grid-shaped. In addition to strengthening the structural strength of the annular wall 101 due to their thickness, they also have an additional function in this design, specifically:

[0037] The adjacent connecting ribs 103 intersect to form rectangular holes that allow airflow to pass through. When the axial flow fan blade 200 is running, the airflow is disturbed by the plate-shaped axial flow fan blade 200. The airflow that is close to it is pushed to the front of the axial flow fan blade 200. At this time, the airflow field at the root of the axial flow fan blade 200 is simultaneously disturbed in the opposite direction. Part of this airflow flows along the back of the axial flow fan blade 200, and the other part rushes towards the noise reduction groove 110 opened in the annular wall 101. After passing through the rectangular holes between the connecting ribs 103, the rectangular holes guide the airflow and blow it to the side of the elastic sheet 105, which efficiently excites the elastic sheet 105 to generate controlled high-frequency micro-amplitude vibration.

[0038] The specific excitation principle is further explained here. When the high-speed but turbulent airflow passes through the rectangular hole of the connecting rib 103, its large-scale vortex is cut and broken by the connecting rib 103, forming a series of highly directional and energy-concentrated periodic micro-jets. These micro-jets act directly on the side of the elastic sheet 105 at a precise angle and with a higher flow velocity. This not only avoids the problem of excessive damping caused by frontal impact, but also forms a high-frequency, high-energy effective pressure pulsation on its surface. This pulsation quickly overcomes the structural damping of the elastic sheet 105 and efficiently excites the elastic sheet 105 to generate strong bending mode vibration at its natural frequency. This forced vibration, in turn, acts on the flow field. Its vibration energy is dissipated through the internal friction of the material and sound radiation. At the same time, the reverse sound wave generated by the vibration of the elastic sheet 105 interferes and cancels out the original aerodynamic noise sound wave in the sound field, thereby realizing the energy dissipation and cancellation of noise at a specific frequency at the source.

[0039] In this design, it is necessary to further explain that the wheel hub body 100 is made of engineering plastic, specifically PBT-GF30 or PA66-GF30, integrally molded using injection molding. Injection molding is a mature existing technology and will not be elaborated here. The PBT-GF30 or PA66-GF30 materials used can be purchased from BASF (China) Co., Ltd. The integrally molded wheel hub body 100 includes a noise reduction groove 110 and a connecting rib 103. In addition to its thickness accounting for 30% of the depth of the noise reduction groove 110, the connecting rib 103 is preferably 1-2mm wide in this design. The diameter of the rectangular holes between adjacent connecting ribs 103 is 3-5mm. This width dimension can optimally disperse the airflow into effective micro-jets while ensuring structural strength.

[0040] In addition, the elastic sheet 105 is preferably made of one of 304 stainless steel, 316 stainless steel and titanium alloy in this solution. The thickness of the elastic sheet 105 is preferably in the range of 0.1-0.3mm. This thickness is mainly selected for household appliances. Its target noise reduction range is 100Hz-2000Hz. This range covers the main aerodynamic noise generated by the rotation of the axial fan blade 200 and the low-to-medium frequency noise generated by structural resonance.

[0041] Regarding the aforementioned back cavity 104, it should be further explained that the volume of the noise reduction groove 110 back cavity 104 and the cross-sectional area of ​​the rectangular aperture together determine the resonant frequency of the Helmholtz resonator. Specifically, this resonant frequency... f The following formula can be used for estimation:

[0042] In the formula, C is the speed of sound, A is the area of ​​the rectangular orifice, V is the volume of the back cavity 104, and L is the effective length of the rectangular orifice. The purpose of the back cavity 104 is to match the main aerodynamic noise frequency generated by the rotation of the axial fan blade 200, such as the passing frequency BPF of the axial fan blade 200 and its harmonics, so as to enhance the absorption effect of noise at this frequency.

[0043] Example 1: Applicable to air purifiers (characterized by medium size, low to medium speed, and a target noise reduction frequency of 620Hz).

[0044] Application product: Air purifier. This product category requires quiet operation, as noise directly affects the user experience.

[0045] Experimental parameters for the 104-cavity back cavity and the rectangular aperture:

[0046] Single noise reduction slot 110 back cavity 104 volume: V=1.5×10 -5 m 3 ;

[0047] Total area of ​​the rectangular hole opening: A = 8.0 × 10 -6 m 2 ;

[0048] Effective length of rectangular hole opening: L=5mm;

[0049] The speed of sound is taken as 340 m / s at room temperature.

[0050] Substituting into the previous formula, the resonant frequency can be calculated. f The result is 603Hz, which is close to the target noise reduction frequency of 620Hz, and can effectively target specific noise peaks of air purifiers.

[0051] Example 2: Applicable to floor fans (large, low speed, target noise reduction frequency of 275Hz).

[0052] Experimental parameters for the 104-cavity back cavity and the rectangular aperture:

[0053] Single noise reduction slot 110 back cavity 104 volume: V=1.2×10 -4 m 3 ;

[0054] Total area of ​​the rectangular hole opening: A = 3.0 × 10 -5 m 2 ;

[0055] Effective length of rectangular hole opening: L=4mm;

[0056] The speed of sound is taken as 340 m / s at room temperature.

[0057] Substituting into the previous formula, the resonant frequency can be calculated. f The result is 296Hz, which is close to the target noise reduction frequency of 275, and can effectively target specific noise peaks of floor fans.

[0058] The working principle is the synergy of structural damping and aeroacoustic effects: First, through the damping effect of the elastic plate 105, the mechanical vibration energy of the hub body 100 and the axial flow fan blade 200 is directly consumed, suppressing structural radiation noise from the source; at the same time, the grid-modulated airflow actively excites the elastic plate 105, and through the Helmholtz resonance effect, they work together on the flow field to absorb and cancel specific aerodynamic noise components. The two mechanisms are physically coupled and functionally complementary, jointly achieving a wide-bandwidth and high-efficiency noise reduction effect.

[0059] In the overall design, the connecting rib 103, the back cavity 104, and the elastic sheet 105 are coupled together, working synergistically to form a hub structure that is efficient, lightweight, and operates with low noise.

[0060] The rectangular openings designed by the grid-like connecting ribs 103 first, together with the back cavity 104, form a Helmholtz resonator targeting a specific aerodynamic noise frequency, performing the first stage of acoustic energy dissipation; more importantly, when the airflow passes through, these openings actively modulate and accelerate the airflow into a series of periodic micro-jets with precise direction and concentrated energy. These micro-jets efficiently excite the wave-shaped elastic sheet 105 to generate forced vibration from the side rather than the front; and the elastic sheet 105, as a damping element, dissipates the mechanical energy of structural vibration from the hub through internal material friction and interface slippage. As an actively driven acoustic element, the vibration generated by the micro-jets in the elastic sheet 105, in turn, modulates the flow field and radiates sound waves, interfering and canceling out the original noise at a specific frequency.

[0061] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A lightweight hub structure with gradient porosity for axial flow fan blades, comprising a hub body (100) and axial flow fan blades (200), characterized in that: The hub body (100) includes an annular wall (101), and the annular wall (101) has an arc-shaped groove (102) circumferentially. The arc-shaped groove (102) includes a mounting groove (109) for mounting the axial flow fan blade (200) and a noise reduction groove (110) for not mounting the axial flow fan blade (200); the opening of the noise reduction groove (110) is provided with a grid-like connecting rib (103), and the noise reduction groove (110) is the same shape as the mounting groove (109); The noise reduction groove (110) has a back cavity (104) formed behind the connecting rib (103) in the depth direction. An elastic sheet (105) is provided inside the back cavity (104), and the two ends of the elastic sheet (105) are connected to the inner wall of the noise reduction groove (110) through a fixing structure.

2. The lightweight hub structure with gradient porosity for axial flow fan blades according to claim 1, characterized in that: The thickness of the connecting rib (103) extending into the noise reduction groove (110) accounts for 25%-35% of the overall depth of the noise reduction groove (110).

3. The lightweight hub structure with gradient porosity for axial flow fan blades according to claim 1, characterized in that: The elastic sheet (105) has a wavy sheet structure. When the elastic sheet (105) is installed in the noise reduction groove (110), the wavy turning point of the elastic sheet (105) contacts the inner wall of the noise reduction groove (110).

4. The lightweight hub structure with gradient porosity for axial flow fan blades according to claim 1, characterized in that: The fixing structure includes an embedding groove formed on the inner wall of the two short sides of the noise reduction groove (110) and a through hole (106) that penetrates the annular wall (101) and communicates with the embedding groove.

5. The lightweight hub structure with gradient porosity for axial flow fan blades according to claim 4, characterized in that: The elastic sheet (105) is provided with fixing blocks (108) with through holes (107) at both ends. The fixing blocks (108) match the embedding groove and the elastic sheet (105) is fixed by fasteners passing through the through holes (107) and the through holes (106).

6. The lightweight hub structure with gradient porosity for axial flow fan blades according to claim 1, characterized in that: The noise reduction groove (110) has multiple connecting ribs (103) at its opening, and these multiple connecting ribs (103) are arranged to intersect each other to form a rectangular hole.

7. The lightweight hub structure with gradient porosity for axial flow fan blades according to claim 1, characterized in that: The wheel hub body (100) is made of either PBT-GF30 or PA66-GF30 engineering plastics and is integrally formed by injection molding. The noise reduction groove (110) and the connecting rib (103) are part of the wheel hub body (100).

8. The lightweight hub structure with gradient porosity for axial flow fan blades according to claim 1, characterized in that: The elastic sheet (105) is made of one of the following materials: 304 stainless steel, 316 stainless steel, and titanium alloy.

9. The lightweight hub structure with gradient porosity for axial flow fan blades according to claim 1, characterized in that: The thickness of the elastic sheet (105) is 0.1-0.3 mm.

10. The lightweight hub structure with gradient porosity for axial flow fan blades according to claim 6, characterized in that: The width of the connecting rib (103) is 1-2 mm, and the diameter of the rectangular hole formed between adjacent connecting ribs (103) is 3-5 mm.

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