Silent centrifugal fan

Abstract

The utility model relates to a mute centrifugal fan, and belongs to the technical field of fans, the mute centrifugal fan comprises a fan shell, an air inlet cover is arranged at an air inlet of the fan shell, the air inlet cover is of a cavity structure and is filled with a sound absorbing material, and a plurality of first through holes allowing sound waves to enter the air inlet cover are formed in the air inlet cover; the air inlet cover is used for covering the air inlet so as to limit the path, perpendicular to the air inlet, of sound waves and airflow, the air inlet of the fan shell is provided with an annular sleeve along the inner wall of the air inlet, the annular sleeve is provided with a first mounting groove used for being filled with sound absorption materials along the circumferential face of the annular sleeve, and the annular sleeve is provided with a first sealing plate used for covering a notch of the first mounting groove along the circumferential face of the annular sleeve. The first sealing plate is provided with a plurality of second through holes allowing sound waves to enter the first mounting groove, the peripheral face of the air inlet cover and the first sealing plate jointly define an air inlet space, and the sound waves can be reflected between the peripheral face of the air inlet cover and the first sealing plate in a reciprocating mode. The sound energy attenuation efficiency is improved, and then the noise reduction effect is improved.

Description

A silent centrifugal fan Technical Field

[0001] This application relates to the field of fan technology, and in particular to a silent centrifugal fan. Background Technology

[0002] Centrifugal fans are widely used in industrial ventilation, air conditioning systems, and equipment cooling due to their compact structure, large air volume, and high efficiency. However, they generate significant noise during operation, which not only affects the comfort of the user environment but may also cause long-term hearing damage to those nearby. Therefore, effective noise reduction technologies are urgently needed to address this issue.

[0003] The main sources of fan noise are twofold: aerodynamic noise (wind noise) and mechanical noise. Aerodynamic noise primarily originates from two sources: first, the intense cutting action between the fan impeller and the air during high-speed rotation generates strong aerodynamic noise within the fan, and this noise energy can propagate to the external environment along the air inlet; second, when external air flows into the fan, the impact and friction with the inner wall of the air inlet or the guide structure also generate additional flow noise. Mechanical noise originates from two sources: first, during fan operation, worn bearings, insufficient lubrication, or poor quality bearings will produce metallic friction noise or vibration noise; second, poor impeller dynamic balance will cause fan vibration, which is transmitted to the structure, generating structural noise.

[0004] In the drying systems of car wash machines, pharmaceutical machinery, and glass machinery, especially in car wash machines, air-drying fans need to achieve air speeds of 40-80 meters per second. The corresponding air pressure is also much higher than that of ordinary fans. The high-speed rotating impeller cuts through the air, generating a large amount of mid-to-high frequency noise (above 1000 Hz). Because mechanical noise is relatively minor compared to industrial fans in these drying systems, the main source of noise is aerodynamic noise.

[0005] To address the above situation, CN112096663A discloses a noise reduction device for a fan inlet. By blocking the direct path of the fan inlet, the airflow direction and sound wave propagation path can be changed, reducing the linear radiation of high-frequency noise. Some sound waves can enter the internal sound-absorbing layer through the perforated cover, while others are reflected by the perforated cover to the guide plate, which then reflects the sound waves back to the perforated cover. Noise reduction is achieved through repeated reflection and absorption of the sound waves. However, this structure only provides sound absorption inside the perforated cover, while one side of the guide plate can only reflect. This means that sound waves can only achieve limited absorption at the perforated cover during propagation, resulting in low sound energy attenuation efficiency and thus a limited noise reduction effect. This is particularly true for fans in applications such as car wash machines and air dryers that require high wind speeds and large air volumes, where the noise reduction effect is not outstanding. Summary of the Invention

[0006] In order to improve the sound energy attenuation efficiency and thus improve the noise reduction effect, this application provides a silent centrifugal fan.

[0007] The silent centrifugal fan provided in this application adopts the following technical solution:

[0008] A silent centrifugal fan includes a fan housing. An air inlet hood is provided at the air inlet of the fan housing. The air inlet hood has a cavity structure and is filled with sound-absorbing material. The air inlet hood has several silencer holes for sound waves to enter its interior. The air inlet hood is used to cover the air inlet to limit the path of sound waves and airflow perpendicular to the air inlet. An annular sleeve is provided along the inner wall of the air inlet of the fan housing. The annular sleeve has a first mounting groove for filling with sound-absorbing material along its circumference. A first sealing plate is provided along the circumference of the annular sleeve for covering the opening of the first mounting groove. The first sealing plate has several first through holes for sound waves to enter the first mounting groove. The circumference of the air inlet hood and the first sealing plate together enclose an air inlet space, and sound waves can be reflected back and forth between the circumference of the air inlet hood and the first sealing plate.

[0009] By adopting the above technical solution, when the fan is running, the impeller's rotation cutting the air generates a large amount of medium- and high-frequency aerodynamic noise. The sound waves propagate along the air inlet direction. First, some sound waves pass through the silencing holes on the air inlet shroud and enter its internal cavity structure, where they are absorbed by the sound-absorbing cotton. Another portion of the sound waves is reflected after hitting the outer surface of the air inlet shroud, but the reflected sound waves can still pass through the first through-hole on the first sealing plate and enter the first mounting groove, where they are absorbed a second time by the sound-absorbing cotton. A portion of the sound waves will continue to be reflected by the first sealing plate, returning to the air inlet shroud and entering the sound-absorbing cotton through the silencing holes for a third absorption. Because the outer wall of the air inlet shroud and the first sealing plate form two opposing reflective surfaces, the sound waves can propagate back and forth repeatedly in this space. Each reflection has the opportunity to enter the sound-absorbing cotton area through the through-hole, forming a composite noise reduction path of multiple reflections and absorptions. Therefore, this is beneficial for improving sound energy attenuation efficiency, thereby improving the noise reduction effect.

[0010] Secondly, the first sealing plate not only reflects sound waves and allows them to penetrate into the sound-absorbing material, but also replaces the guide plate to guide airflow. Furthermore, when high-speed air collides or rubs against the first sealing plate at the air inlet, generating additional flow noise, some of this noise can be directly absorbed by the sound-absorbing material in the first mounting groove through the first through-hole on the first sealing plate. Therefore, this technical solution can balance high-speed airflow efficiency with low-noise operation requirements, making it particularly suitable for dry wind farms with extremely high wind speed requirements.

[0011] Optionally, the inner peripheral wall of the fan housing is provided with a second mounting groove for filling sound-absorbing material, and a second sealing plate is provided inside the fan housing for covering the opening of the second mounting groove, and the second sealing plate is provided with a plurality of second through holes.

[0012] By adopting the above technical solution, since the structure is arranged close to the rotating area of ​​the fan impeller, it can directly absorb the high-frequency noise generated by the core of the fan, reduce the propagation intensity of noise inside the fan casing, and form a first-level noise reduction system that absorbs noise inside the fan casing, a second-level noise reduction system that absorbs sound waves inside the air inlet hood, and a third-level noise reduction system that repeatedly reflects noise between the air inlet hood and the first sealing plate and absorbs noise through sound-absorbing materials, thus constructing a multi-level, three-dimensional noise reduction system that significantly improves noise reduction efficiency.

[0013] Optionally, the annular sleeve includes an annular horizontal portion for supporting and fixing the top of the fan housing. The annular horizontal portion is connected to a first annular inclined portion via a first arc guide surface. The first annular inclined portion is inclined toward the center line of the air inlet. The first annular inclined portion is connected to an annular recess, which forms the first mounting groove. The annular recess is connected to a second annular inclined portion. The second annular inclined portion is connected to an annular vertical portion via a second arc guide surface. The second annular inclined portion is inclined toward the center line of the air inlet. One side of the first sealing plate is fixed to the first annular inclined portion, and the other side is fixed to the second annular inclined portion.

[0014] By adopting the above technical solution, the annular horizontal part is used to support and position the top of the fan casing, which facilitates the rapid installation and disassembly of the overall structure. It has good versatility and maintainability. The upper side of the first sealing plate can be erected and fixed on the first annular inclined part, and the lower side of the second sealing plate can be erected and fixed on the second annular inclined part. The first and second annular inclined parts not only serve as fixed support components for the first sealing plate, but also automatically drive and determine the tilt angle of the first sealing plate during the component installation process. Therefore, there is no need to manually adjust the angle of the first sealing plate, which not only improves the assembly efficiency, but also ensures the consistency of the guide angle.

[0015] The design of the first and second circular arc guide surfaces ensures that when airflow enters the fan from the outside, it no longer forms sharp deflections or turbulent collisions with the structural edges. Instead, it gradually changes direction through smooth bevels, achieving streamlined airflow guidance. Furthermore, the first sealing plate is positioned precisely between the two bevels, tilted at a certain angle, forming a harmonious guiding surface with the circular arc guide surfaces. This allows the airflow to transition smoothly and enter the fan impeller area, thereby reducing flow noise and energy loss. Simultaneously, this guiding path avoids local dead zones and sound wave retention areas, improving the efficiency of sound wave reflection and absorption.

[0016] The annular vertical section is equivalent to adding a short guide section to the airflow. This helps to alleviate the turbulence and secondary eddies generated when the airflow enters the fan casing in an annular and oblique manner. It also helps to make the airflow enter the impeller area more stably. For high wind speed systems, it helps to control the vortex structure and reduce the additional noise caused by turbulence.

[0017] Optionally, the side and bottom surfaces of the annular recess are transitioned by a third circular arc guide surface, and the bottom surface of the annular recess is recessed away from the air outlet.

[0018] By adopting the above technical solution, the third arc guide surface avoids the sharp angle or right angle structure of the first mounting groove. Sound-absorbing cotton is often a flexible material, and the sharper the edges and corners, the more difficult it is to fill. The design of the third arc guide surface improves the filling density and structural stability.

[0019] The recessed structure increases the space of the first mounting groove, thereby increasing the filling volume of the sound-absorbing material, which is equivalent to thickening the sound-absorbing layer. The thicker the sound-absorbing material, the stronger its ability to attenuate mid-to-low frequency noise, and the wider the overall noise reduction frequency band, which is conducive to improving the noise reduction effect.

[0020] From the perspective of the inner cavity of the fan casing, the bottom surface of the annular recess is equivalent to a convex arc surface. When the convex structure encounters sound waves, it will reflect and diffuse the sound waves in multiple directions, rather than reflecting them in a single direction like a mirror. This diffusion makes the propagation path of the sound waves random, which makes it easier for the sound-absorbing material in the second mounting slot to fully absorb the sound.

[0021] Moreover, the raised arc surface can disrupt the reflection path of the parallel surface, causing the sound waves to disperse, thereby reducing the reverberation enhancement of specific frequencies, thus reducing the sharp noise emitted by the fan and further improving the noise reduction effect.

[0022] Optionally, the air inlet hood includes an upper cover plate, an annular connecting portion, a conical side portion of the hood body, and a cylindrical side portion of the hood body. The upper cover plate covers the air inlet, the annular connecting portion is connected to the upper cover plate, and the annular connecting portion is connected to the conical side portion of the hood body through a fourth arc guide surface. The bottom surface of the conical side portion of the hood body is connected to the cylindrical side portion of the hood body. The bottom area of ​​the conical side portion of the hood body is smaller than its top area. Sound-absorbing material is filled in the cavity of the conical side portion of the hood body and the cylindrical side portion of the hood body. A plurality of first through holes are formed on the cylindrical side portion of the hood body and the conical side portion of the hood body. The conical side portion of the hood body is parallel to the first sealing plate, and the cylindrical side portion of the hood body is parallel to the annular vertical portion.

[0023] By adopting the above technical solution, the upper cover plate acts as a vertical flow path to block the airflow. When the airflow flows along the path of the upper cover plate, the annular connecting part and the conical side of the cover body, it can achieve flexible deflection at the fourth arc guide surface, reduce flow impact noise, and thus improve the overall aerodynamic stability and noise reduction performance.

[0024] The conical side of the enclosure is wider at the top and narrower at the bottom, and is parallel to the first sealing plate. This creates a ring-shaped conical airflow channel between the conical side and the first sealing plate, while a cylindrical vertical airflow channel is formed between the cylindrical side and the ring-shaped vertical section. After entering through the inlet, the airflow first enters the conical channel. As the channel contracts, the airflow is gradually constricted and deflected downwards, reducing turbulence and effectively improving airflow uniformity and stability. Furthermore, the gradually contracting conical space prevents sudden collisions or swirling of the airflow in its flow path, reducing impact on the structural surface and helping to reduce flow noise.

[0025] Moreover, the parallel alignment of the conical side of the cover with the first sealing plate helps to increase the number of sound wave reflections, allowing more sound waves to be absorbed by the sound-absorbing materials inside and outside the annular conical air guide channel, further improving the noise reduction effect.

[0026] After passing through the conical channel, the airflow further enters the cylindrical channel, which allows the airflow to enter the impeller area of ​​the fan in a relatively stable path, preventing disturbances or secondary noise caused by abrupt changes in shape.

[0027] Optionally, the annular connecting portion and the upper cover plate are connected by a plurality of connectors, and the plurality of connectors are also connected to the annular horizontal portion and the fan casing.

[0028] By adopting the above technical solution, one connector can connect multiple components at the same time, effectively reducing assembly complexity and manual installation time.

[0029] Optionally, the upper cover plate, the fan housing, and the annular sleeve are all made of PE material. The first sealing plate and the annular sleeve, and the second sealing plate and the fan housing are all connected by anchor bolts. The connecting piece is a C-shaped steel. The C-shaped steel is connected to the upper cover plate and the fan housing by bolts. The C-shaped steel and the upper cover plate together abut against the annular connecting part, and the C-shaped steel and the fan housing together abut against the annular horizontal part.

[0030] By adopting the above technical solution, PE material possesses certain flexibility and good mechanical damping characteristics, which can effectively absorb mechanical vibration and high-frequency sound waves, reducing structural noise transmitted through the shell structure. The first sealing plate and the annular sleeve, as well as the second sealing plate and the fan casing, are all connected by anchor bolts. The air inlet hood is positioned by C-shaped steel, the upper cover plate, the fan casing, the annular connecting part, and the annular horizontal part, achieving a detachable connection structure for the entire system. This is beneficial for improving production and assembly efficiency and facilitates the replacement of sound-absorbing materials.

[0031] Optionally, an exhaust nozzle is provided protruding from the circumferential surface of the fan housing, and an inclined connecting surface is provided on the circumferential surface of the fan housing. The root of the exhaust nozzle away from its exhaust port is connected to the bottom of the fan housing through the inclined connecting surface. The exhaust nozzle is connected to the inclined connecting surface through a fifth arc guide surface. The second mounting groove is located between the exhaust nozzle and the blade drive component. The two sides of the root of the exhaust nozzle away from its exhaust port are connected to the circumferential surface of the fan housing through a sixth arc guide surface.

[0032] By adopting the above technical solution, the design of the inclined connecting surface, and the location of the second mounting groove, the air noise generated at the impeller cannot pass through the exhaust nozzle in a straight line, but needs to go through at least one deflection or reflection before it can be discharged from the exhaust nozzle, which helps to further improve the noise reduction effect.

[0033] The combined action of the fifth and sixth circular arc guide surfaces makes the high-speed airflow transition more smoothly when it changes direction and is discharged, keeping the air duct unobstructed and not reducing exhaust efficiency. At the same time, it softens the exhaust air and helps to optimize the overall quiet performance.

[0034] Optionally, the exhaust nozzle has an annular mounting groove for filling with sound-absorbing material, and the inner wall of the exhaust nozzle is fitted with a third sealing plate for covering the opening of the annular mounting groove. The third sealing plate has several third through holes.

[0035] By adopting the above technical solution, sound waves can also be bounced and absorbed several times at the exhaust nozzle, further improving the noise reduction effect.

[0036] Optionally, the air guiding surface of the first sealing plate is an arc surface, and the air guiding surface of the first sealing plate protrudes towards the center of the air inlet. The conical side of the cover body is a curved cone, and the circumference of the conical side of the cover body is concave in the direction of its central axis.

[0037] By adopting the above technical solution, the conical side of the cover body with the curved conical structure and the arc-shaped second sealing plate can make the airflow path more gentle during the process of being introduced from the air inlet, reduce the sharp turns and deflection angles of the streamline, thereby reducing the excitation of turbulence and shear noise;

[0038] Furthermore, the curved air guide surface and curved cone structure make it easier for sound waves to undergo multi-directional scattering and energy dissipation during reflection, thereby weakening standing waves and resonance phenomena and further improving the attenuation efficiency of sound waves. Therefore, the curved air guide surface and curved cone structure can not only guide the airflow smoothly through structural transitions, but also disperse and break up disturbed sound energy at the acoustic level, thus significantly improving the overall quietness performance of the fan during operation.

[0039] In summary, this application includes at least one of the following beneficial technical effects:

[0040] 1. Two opposing reflective surfaces are formed between the outer wall of the air inlet hood and the first sealing plate. Sound waves can propagate back and forth repeatedly in this space. Each reflection has the opportunity to enter the sound-absorbing cotton area through the through-hole, forming a composite noise reduction path of multiple reflections and multiple absorptions. Therefore, it is beneficial to improve the sound energy attenuation efficiency, thereby improving the noise reduction effect;

[0041] 2. The first sealing plate not only serves to reflect sound waves and allow sound waves to penetrate into the sound-absorbing material, but also replaces the guide plate to guide the airflow. Moreover, when high-speed air collides or rubs against the first sealing plate at the air inlet, generating additional flow noise, some of this noise can be directly absorbed by the sound-absorbing material in the first mounting groove through the second through hole on the first sealing plate. Therefore, it can balance the airflow efficiency under high wind speed with the requirements of low noise operation, and is particularly suitable for dry wind farms with extremely high wind speed requirements.

[0042] 3. Because the structure is arranged close to the rotating area of ​​the fan impeller, it can directly absorb the high-frequency noise generated by the core of the fan, reduce the propagation intensity of noise inside the fan casing, and form a first-level noise reduction that absorbs noise inside the fan casing, a second-level noise reduction that absorbs sound waves inside the air inlet hood, and a third-level noise reduction that involves repeated reflection between the air inlet hood and the first sealing plate and noise absorption through sound-absorbing materials. This creates a multi-level, three-dimensional noise reduction system that significantly improves noise reduction efficiency.

[0043] 4. At each turning point of the airflow, a circular arc guide surface is used for transition. A ring-shaped conical airflow channel, wider at the top and narrower at the bottom, is formed between the conical side of the shroud and the first sealing plate, while a cylindrical vertical airflow channel is formed between the cylindrical side of the shroud and the ring-shaped vertical section. After entering through the air inlet, the airflow first enters the conical channel, which is wider at the top and narrower at the bottom. As the channel contracts, the airflow is gradually constricted and deflected downwards, reducing the formation of turbulence and effectively improving the uniformity and stability of the airflow. Furthermore, the gradually contracting conical space avoids sudden collisions or swirling of the airflow in the flow path, reducing impact on the structural surface. This not only guides the airflow smoothly, reducing energy consumption, but also helps to reduce flow noise.

[0044] 5. From the perspective of the fan casing's inner cavity, the bottom surface of the annular recess is equivalent to a convex arc surface. When sound waves encounter this convex structure, it reflects and diffuses the sound waves in multiple directions, rather than reflecting them mirror-like in a single direction. This diffusion randomizes the sound wave propagation path, facilitating full absorption by the sound-absorbing material in the second mounting slot. Furthermore, the convex arc surface disrupts the parallel reflection path, scattering the sound waves and thus reducing the reverberation enhancement at specific frequencies. This reduces the sharp noise emitted by the fan, further improving the noise reduction effect. Attached Figure Description

[0045] Figure 1 is a schematic diagram of the overall structure of Embodiment 1 of this application.

[0046] Figure 2 is a structural schematic diagram of Embodiment 1 of this application, illustrating the mounting port and the first inclined portion.

[0047] Figure 3 is a structural schematic diagram of Embodiment 1 of this application, illustrating the air inlet and the second sealing plate.

[0048] Figure 4 is a schematic diagram of the structure of the annular sleeve in Embodiment 1 of this application.

[0049] Figure 5 is a structural schematic diagram of Embodiment 1 of this application, illustrating the first mounting groove.

[0050] Figure 6 is an enlarged schematic diagram of part A in Figure 5.

[0051] Figure 7 is an enlarged schematic diagram of part B in Figure 5.

[0052] Figure 8 is a structural schematic diagram of Embodiment 1 of this application, illustrating the air inlet shroud.

[0053] Figure 9 is a schematic diagram of the structure of the exhaust nozzle in Embodiment 2 of this application.

[0054] Figure 10 is a structural schematic diagram of Embodiment 2 of this application, illustrating the air inlet shroud and the first sealing plate.

[0055] Explanation of reference numerals in the attached drawings: 1. Fan housing; 11. Air inlet; 12. Mounting port; 13. Exhaust nozzle; 131. Annular mounting groove; 14. Inclined connecting surface; 15. Fifth arc guide surface; 16. Sixth arc guide surface; 17. Protrusion; 171. Second mounting groove; 2. Second sealing plate; 21. Second through hole; 3. Annular sleeve; 31. Annular horizontal part; 32. First arc guide surface; 33. First annular inclined part; 34. Annular recess; 3 41. First mounting groove; 342. Third arc guide surface; 35. Second annular inclined part; 36. Second arc guide surface; 37. Annular vertical part; 4. First sealing plate; 41. First through hole; 5. Air inlet hood; 51. Top cover plate; 52. Annular connecting part; 53. Conical side of the hood body; 54. Columnar side of the hood body; 55. Fourth arc guide surface; 56. Silencing hole; 6. Connector; 61. C-shaped steel; 7. Third sealing plate; 71. Third through hole. Detailed Implementation

[0056] The present application will be further described in detail below with reference to Figures 1-10.

[0057] Example 1

[0058] Embodiment 1 of this application discloses a silent centrifugal fan.

[0059] As shown in Figures 1, 2, and 3, the silent centrifugal fan includes a fan housing 1. The top of the fan housing 1 has an air inlet 11, and the bottom of the fan housing 1 has a mounting port 12 for installing a drive motor. An exhaust nozzle 13 protrudes from the circumference of the fan housing 1, and the exhaust nozzle 13 is integrally formed with the fan housing 1. The exhaust nozzle 13 is strip-shaped, and both sides of the exhaust nozzle 13 are curved. The top surface of the exhaust nozzle 13 is flush with and connected to the top surface of the fan housing 1. An inclined connecting surface 14 is provided on the circumferential portion of the fan housing 1 below the exhaust nozzle 13. The inclined connecting surface 14 slopes downwards towards the mounting port 12, and the top side of the inclined connecting surface 14 connects to the bottom of the base of the exhaust nozzle 13 via a fifth arc guide surface 15. Both sides of the exhaust nozzle 13 connect to the fan housing 1 via a sixth arc guide surface 16. A protrusion 17 is provided along the circumferential contour of the fan housing 1, forming a second mounting groove 171 for filling sound-absorbing material on the inner sidewall of the fan housing 1. The width of the two ends of the protrusion 17 gradually decreases near the exhaust nozzle 13, making the two ends of the protrusion 17 pointed, and the depth of the corresponding second mounting groove 171 at both ends of the protrusion 17 gradually decreases. The exhaust nozzle 13 is set higher than the protrusion 17, so that the second mounting groove 171 is located between the exhaust nozzle 13 and the blade drive component (motor). A second sealing plate 2 is fixedly connected inside the fan housing 1 by anchors. The second sealing plate 2 is used to cover the opening of the second mounting groove 171. The upper side of the second sealing plate 2 is fixed to the inner wall of the housing above the second mounting groove 171, and the lower side of the second sealing plate 2 is fixed to the inner wall of the housing below the second mounting groove 171. The second sealing plate 2 has several second through holes 21. A mounting plate is fixed to the mounting port 12 of the fan casing 1 by bolts. The motor is mounted on the mounting plate, and the motor shaft extends into the fan casing 1 and is connected to the impeller.

[0060] Figures 4, 5, 6, and 7 show that the air inlet 11, the circumferential surface of the fan housing 1, and the mounting port 12 are coaxial. An annular sleeve 3 is fitted over the air inlet 11 of the fan housing 1. The annular sleeve 3 includes an annular horizontal portion 31, which is coaxial with the air inlet 11 and supported on the top surface of the fan housing 1 by bolts. A first annular inclined portion 33 is connected to the annular horizontal portion 31 along its inner side via a first arc guide surface 32. The first annular inclined portion 33 is an inverted conical annular shape with a larger top diameter and a smaller bottom diameter. The extended generatrix of the first annular inclined portion 33 intersects the central axis of the air inlet 11. An annular recess 34 is connected to the lower side of the first annular inclined portion 33. The concave space of the annular recess 34 forms the first mounting groove 341 of the annular sleeve 3, which is filled with sound-absorbing material. A second annular inclined portion 35 is connected to the side of the bottom surface of the annular recess 34 facing the central axis of the air inlet 11. The second annular inclined portion 35 is also an inverted conical annular shape with a larger top diameter and a smaller bottom diameter, and the side of the second annular inclined portion 35 facing the air inlet 11 is coplanar with the side of the first annular inclined portion 33 facing the air inlet 11. An annular vertical portion 37 is connected to the second annular inclined portion 35 via a second arc guide surface 36. The annular vertical portion 37 is coaxial with the air inlet 11, and the diameter of the annular vertical portion 37 is smaller than the diameter of the bottom of the second annular inclined portion 35.

[0061] The longitudinal section of the annular recess 34 consists of two L-shaped plates arranged opposite each other. The vertical section of the annular recess 34 is inclined away from the central axis of the air inlet 11, that is, the vertical section of the annular recess 34 is conical and annular. The transverse section of the annular recess 34 is connected to its vertical section through a third circular arc guide surface 342. Furthermore, the transverse section (i.e., the bottom surface) of the annular recess 34 is an arc surface that is recessed away from the outlet.

[0062] The first annular inclined portion 33 and the second annular inclined portion 35 are connected together by anchor bolts to a first sealing plate 4. The upper side of the first sealing plate 4 rests on the first annular inclined portion 33, and the lower side of the first sealing plate 4 rests on the second annular inclined portion 35. The first sealing plate 4 is an inverted conical annular plate, and the first sealing plate 4 has several first through holes 41.

[0063] As shown in Figure 8, an air inlet shroud 5 is provided at the air inlet 11 of the fan casing 1. The air inlet shroud 5 includes an upper cover plate 51, an annular connecting part 52, a conical side part 53 of the shroud body, and a cylindrical side part 54 of the shroud body. The upper cover plate 51 is a circular plate that covers the air inlet 11 and the two are coaxial. The annular connecting part 52 is coaxial with the upper cover plate 51 and is connected by anchors. The annular connecting part 52 is connected to the conical side part 53 of the shroud body through a fourth arc guide surface 55. Next, the bottom surface of the conical side 53 of the cover body is connected to the cylindrical side 54 of the cover body. The bottom area of ​​the conical side 53 of the cover body is smaller than its top area. The sound-absorbing material is filled in the cavity of the conical side 53 and the cylindrical side 54 of the cover body. Several sound-absorbing holes 56 are opened on the cylindrical side 54 and the conical side 53 of the cover body. The conical side 53 of the cover body is parallel to the first sealing plate 4, and the cylindrical side 54 of the cover body is parallel to the annular vertical part 37.

[0064] As shown in Figure 1, the annular connecting part 52 and the upper cover plate 51 are connected by several connecting parts 6, and the connecting parts 6 are also connected to the annular horizontal part 31 and the fan casing 1. The upper cover plate 51, the fan casing 1 and the annular sleeve 3 are all made of PE material. The first sealing plate 4 and the annular sleeve 3, and the second sealing plate 2 and the fan casing 1 are all connected by anchor bolts. The connecting parts 6 are C-shaped steel 61. The C-shaped steel 61 is connected to the upper cover plate 51 and the fan casing 1 by bolts. The C-shaped steel 61 and the upper cover plate 51 together abut against the annular connecting part 52, and the C-shaped steel 61 and the fan casing 1 together abut against the annular horizontal part 31.

[0065] The implementation principle of this application embodiment is as follows: When the fan is running, the impeller rotation cutting the air generates a large amount of medium and high frequency aerodynamic noise. The sound waves propagate along the direction of the air inlet 11. First, a portion of the sound waves will pass through the silencing holes 56 on the air inlet shroud 5 and enter its internal cavity structure, where they will be absorbed for the first time by the sound-absorbing cotton. Another portion of the sound waves will be reflected after hitting the outer surface of the air inlet shroud 5, but the reflected sound waves can still pass through the first through hole 41 on the first sealing plate 4 and enter the first mounting groove 341, where they will be absorbed for the second time by the sound-absorbing cotton. A portion of the sound waves will continue to be reflected by the first sealing plate 4 and return to the air inlet shroud 5, entering the sound-absorbing cotton through the silencing holes 56 to complete the third absorption. Since the outer wall of the air inlet shroud 5 and the first sealing plate 4 form two opposing reflective surfaces, the sound waves can propagate back and forth repeatedly in this space. Each reflection has the opportunity to enter the sound-absorbing cotton area through the through hole, forming a composite noise reduction path of multiple reflections and multiple absorptions. Therefore, it is beneficial to improve the sound energy attenuation efficiency, thereby improving the noise reduction effect.

[0066] Secondly, the first sealing plate 4 not only serves to reflect sound waves and allow them to penetrate into the sound-absorbing material, but also replaces the guide plate to guide airflow. Furthermore, when high-speed air collides or rubs against the first sealing plate 4 at the air inlet 11, generating additional flow noise, some of this noise can be directly absorbed by the sound-absorbing material in the first mounting groove 341 through the first through-hole 41 on the first sealing plate 4. Therefore, this technical solution can balance high-speed airflow efficiency with low-noise operation requirements, making it particularly suitable for dry wind farms with extremely high wind speed requirements.

[0067] Because the structure is arranged close to the rotating area of ​​the fan impeller, it can directly absorb the high-frequency noise generated by the core of the fan, reduce the propagation intensity of the noise inside the fan casing 1, and form a first-level noise reduction system that absorbs noise inside the fan casing 1, a second-level noise reduction system that absorbs sound waves inside the air inlet shroud 5, and a third-level noise reduction system that repeatedly reflects noise between the air inlet shroud 5 and the first sealing plate 4 and absorbs noise through sound-absorbing materials. This creates a multi-level, three-dimensional noise reduction system that significantly improves noise reduction efficiency.

[0068] Example 2

[0069] Referring to Figures 9 and 10, the difference between this embodiment and embodiment 1 is that the inner sidewall of the exhaust nozzle 13 is provided with an annular mounting groove 131 for filling with sound-absorbing material, and the inner wall of the exhaust nozzle 13 is provided with a third sealing plate 7 for covering the opening of the annular mounting groove 131. The third sealing plate 7 is provided with a plurality of third through holes 71.

[0070] The air guiding surface of the first sealing plate 4 is an arc surface, that is, the generatrix of the cone-shaped ring formed by the first sealing plate 4 is an arc. The air guiding surface of the first sealing plate 4 protrudes towards the center of the air inlet 11, and the cone-shaped side 53 of the cover body is a curved cone, with the circumference of the cone-shaped side 53 of the cover body concave inward towards its central axis.

[0071] The implementation principle of Example 2 is as follows: sound waves can also be bounced and absorbed several times at the exhaust nozzle 13, further improving the noise reduction effect. The conical side 53 of the cover body with a curved conical structure and the arc-shaped second sealing plate 2 can make the airflow path smoother during the introduction from the air inlet 11, reduce the sharp turns and deflection angles of the streamline, thereby reducing the excitation of turbulence and shear noise;

[0072] Furthermore, the curved air guide surface and curved cone structure make it easier for sound waves to undergo multi-directional scattering and energy dissipation during reflection, thereby weakening standing waves and resonance phenomena and further improving the attenuation efficiency of sound waves. Therefore, the curved air guide surface and curved cone structure can not only guide the airflow smoothly through structural transitions, but also disperse and break up disturbed sound energy at the acoustic level, thus significantly improving the overall quietness performance of the fan during operation.

[0073] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A silent centrifugal fan, characterized in that: The fan housing (1) includes an air inlet hood (5) at its air inlet (11). The air inlet hood (5) is a hollow structure filled with sound-absorbing material. The air inlet hood (5) has several sound-absorbing holes (56) for sound waves to enter it. The air inlet hood (5) is used to cover the air inlet (11) to limit the path of sound waves and airflow perpendicular to the air inlet (11). The air inlet (11) of the fan housing (1) has an annular sleeve (3) along its inner wall. A first mounting groove (341) for filling sound-absorbing material is provided along its circumference. The annular sleeve (3) is provided with a first sealing plate (4) for covering the opening of the first mounting groove (341) along its circumference. The first sealing plate (4) has a plurality of first through holes (41) for sound waves to enter the first mounting groove (341). The air inlet space is jointly enclosed between the circumference of the air inlet hood (5) and the first sealing plate (4). Sound waves can be reflected back and forth between the circumference of the air inlet hood (5) and the first sealing plate (4).

2. The silent centrifugal fan according to claim 1, characterized in that: The inner peripheral wall of the fan housing (1) is provided with a second mounting groove (171) for filling with sound-absorbing material. The fan housing (1) is provided with a second sealing plate (2) for covering the opening of the second mounting groove (171). The second sealing plate (2) is provided with a plurality of second through holes (21).

3. The silent centrifugal fan according to claim 2, characterized in that: The annular sleeve (3) includes an annular horizontal part (31), which is used to support and fix the top of the fan housing (1). The annular horizontal part (31) is connected to a first annular inclined part (33) through a first arc guide surface (32). The first annular inclined part (33) is inclined toward the center line of the air inlet (11). The first annular inclined part (33) is connected to an annular recess (34), which forms the first mounting groove (341). The annular recess (34) is connected to a second annular inclined part (35). The second annular inclined part (35) is connected to an annular vertical part (37) through a second arc guide surface (36). The second annular inclined part (35) is inclined toward the center line of the air inlet (11). One side of the first sealing plate (4) is fixed on the first annular inclined part (33), and the other side is fixed on the second annular inclined part (35).

4. The silent centrifugal fan according to claim 3, characterized in that: The side and bottom surfaces of the annular recess (34) are transitioned by a third arc guide surface (342), and the bottom surface of the annular recess (34) is recessed away from the air outlet.

5. The silent centrifugal fan according to any one of claims 3 or 4, characterized in that: The air inlet hood (5) includes an upper cover plate (51), an annular connecting part (52), a conical side part (53) of the hood body, and a cylindrical side part (54) of the hood body. The upper cover plate (51) covers the air inlet (11). The annular connecting part (52) is connected to the upper cover plate (51). The annular connecting part (52) is connected to the conical side part (53) of the hood body through a fourth arc guide surface (55). The bottom surface of the conical side part (53) of the hood body is connected to the cylindrical side part (54) of the hood body. The bottom area of ​​the conical side (53) of the cover body is smaller than its top area. The sound-absorbing material is filled in the cavity of the conical side (53) and the cylindrical side (54) of the cover body. A plurality of the sound-absorbing holes (56) are opened on the cylindrical side (54) and the conical side (53) of the cover body. The conical side (53) of the cover body is parallel to the first sealing plate (4), and the cylindrical side (54) of the cover body is parallel to the annular vertical part (37).

6. The silent centrifugal fan according to claim 5, characterized in that: The annular connecting part (52) and the upper cover plate (51) are connected by a number of connectors (6), and the number of connectors (6) are also connected to the annular horizontal part (31) and the fan casing (1).

7. The silent centrifugal fan according to claim 6, characterized in that: The upper cover plate (51), the fan housing (1), and the annular sleeve (3) are all made of PE material. The first sealing plate (4) and the annular sleeve (3), and the second sealing plate (2) and the fan housing (1) are all connected by anchors. The connecting piece (6) is a C-shaped steel (61). The C-shaped steel (61) is connected to the upper cover plate (51) and the fan housing (1) by bolts. The C-shaped steel (61) and the upper cover plate (51) together abut against the annular connecting part (52). The C-shaped steel (61) and the fan housing (1) together abut against the annular horizontal part (31).

8. The silent centrifugal fan according to claim 5, characterized in that: The fan housing (1) has an exhaust nozzle (13) protruding from its circumference. The fan housing (1) has an inclined connecting surface (14) on its circumference. The exhaust nozzle (13) is connected to the bottom of the fan housing (1) at its root away from its exhaust port through the inclined connecting surface (14). The exhaust nozzle (13) is connected to the inclined connecting surface (14) through the fifth arc guide surface (15). The second mounting groove (171) is located between the exhaust nozzle (13) and the blade drive component. The exhaust nozzle (13) is connected to the fan housing (1) at both sides of its root away from its exhaust port through the sixth arc guide surface (16).

9. The silent centrifugal fan according to claim 8, characterized in that: The exhaust nozzle (13) has an annular mounting groove (131) for filling with sound-absorbing material. The inner wall of the exhaust nozzle (13) is fitted with a third sealing plate (7) for covering the opening of the annular mounting groove (131). The third sealing plate (7) has several third through holes (71).

10. The silent centrifugal fan according to claim 9, characterized in that: The air guiding surface of the first sealing plate (4) is an arc surface, and the air guiding surface of the first sealing plate (4) protrudes towards the center of the air inlet (11). The conical side (53) of the cover body is a curved cone, and the circumference of the conical side (53) of the cover body is concave in the direction of its central axis.

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