Noise reduction type centrifugal fan structure

Abstract

The invention discloses a noise reduction type centrifugal fan structure and relates to the technical field of centrifugal fans. A first volute tongue part is arranged at the joint of an air outlet and a shell, a second volute tongue part is arranged at the tail end of the first volute tongue part, and the second volute tongue part inclines towards the side close to an impeller, so that a gap between a volute tongue and the impeller is further reduced; the air accelerated by the centrifugal force of the impeller is prevented from entering the shell again through the gap to affect the operation efficiency of the fan, a plurality of flow guide pieces are arranged on the side, close to the impeller, of the second volute tongue part at equal intervals, and a flow guide channel is formed between every two adjacent flow guide pieces. The width of the flow guide piece is gradually increased in the gas flowing direction, so that the flow guide channel is gradually reduced in the gas flowing direction, and when part of gas enters the shell through the gap, the flow speed of the gas can be increased through the flow guide channel; pressure exchange between gas entering the shell through the space between the volute tongue and the impeller and accelerated gas in the shell is avoided, and periodic pulses are formed.

Description

Technical Field

[0001] The present invention relates to the technical field of centrifugal fans, and specifically to a noise-reducing centrifugal ventilation fan structure. Background Art

[0002] A centrifugal fan is a fluid machine widely used in industries, buildings, air conditioners, mines, tunnel ventilation and other fields. Its main function is to pressurize and transport gas through the centrifugal force generated by the rotation of the impeller. However, the centrifugal fan will generate significant noise pollution during operation, affecting the working environment and the health of personnel. Therefore, noise reduction technology has become an important direction for the design and optimization of centrifugal fans.

[0003] Chinese Patent (CN111997935A) discloses a noise-reducing volute tongue structure and a centrifugal fan, specifically disclosing that: the volute tongue structure includes a volute tongue body formed by the shell wall at the connection between the volute and the air outlet, and a plurality of raised blocks on the top of the volute tongue body. The plurality of raised blocks are arranged in sequence along the axis direction of the volute, and an air flow channel for air flow to pass through is provided between adjacent raised blocks.

[0004] In the prior art, raised blocks are arranged at the volute tongue position to reduce the pressure gradient of the air flow near the volute tongue and suppress the superposition of noise in the volute tongue area, thereby reducing the noise of the centrifugal fan. However, the arrangement of the raised blocks can only reduce a part of the pressure gradient. After the air flow collides with the volute tongue, the air flow velocity will decrease, resulting in a large velocity difference between some of the air flow and the accelerated air flow after re-entering the volute interior, and further leading to an increase in the pressure difference. Therefore, how to reduce the gas pressure difference and flow velocity difference at the volute tongue position to achieve noise reduction has become an urgent technical problem to be solved. Summary of the Invention

[0005] The purpose of the present invention is to provide a noise-reducing centrifugal ventilation fan structure to solve the problems raised in the prior art.

[0006] To achieve the above purpose, the present invention provides the following technical solutions:

[0007] A noise reduction type centrifugal fan structure includes a housing and an impeller rotatably driven by a driving component inside the housing. The distance between the inner wall of the housing and the outer edge of the impeller gradually increases along the rotation direction of the impeller, aiming to avoid a large pressure gradient of the air flow inside the housing, which may cause excessive noise. An air inlet and an air outlet are respectively provided in the axial and radial directions of the housing. The axially installed air inlet allows external gas to enter the housing, and the gas is discharged through the radially installed air outlet under the action of the centrifugal force generated by the rotation of the impeller. A rectifying component is provided at the position of the air inlet to guide the inflowing gas. Through the design of the rectifying component, the air flow entering the housing becomes smoother. At the same time, the flow direction of the gas entering the housing is guided, eliminating the intake vortex, reducing the impact between the air flow and the impeller, thereby reducing noise and improving the operating efficiency of the fan;

[0008] A first volute tongue part is provided at the connection between the air outlet and the housing. A second volute tongue part is provided at the end of the first volute tongue part. The second volute tongue part is smoothly connected to the first volute tongue part on the side close to the air outlet to avoid a sudden change in the cross-section at the air outlet, which may cause a sudden change in the flow velocity of the air flow at the air outlet. The second volute tongue part is inclined towards the impeller side to further reduce the gap between the volute tongue and the impeller, preventing the gas accelerated by the centrifugal force of the impeller from re-entering the housing through the gap, which may affect the operating efficiency of the fan. A plurality of guide components are equidistantly arranged on the side of the second volute tongue part close to the impeller, and a guide channel is formed between two adjacent guide components;

[0009] The width of the guide component gradually increases along the gas flow direction, so that the guide channel gradually decreases along the gas flow direction. The purpose is that when a small amount of gas re-enters the housing through the gap, the flow velocity of the gas can be increased by using the guide channel, thereby avoiding pressure exchange between the gas entering the housing through the gap between the volute tongue and the impeller and the gas accelerated inside the housing, forming a periodic pulse, and realizing the function of noise reduction.

[0010] According to the above technical solution, a resonance cavity is provided inside the first volute tongue part. A resonance plate is installed inside the resonance cavity along the radial direction of the housing through a connecting component. When the gas accelerated by the centrifugal force of the impeller impacts the volute tongue, the resonance cavity and the resonance plate inside it vibrate, thereby offsetting the overall vibration of the volute tongue and reducing the noise generated by the air flow impacting the volute tongue at the air outlet.

[0011] According to the above technical solution, the inside of the resonance cavity is in a vacuum state. By evacuating the resonance cavity, the propagation of the sound generated by the vibration of the resonance plate inside the resonance cavity is blocked. The connecting component is an elastic connecting component, and its purpose is also to weaken the propagation of the sound generated by the vibration of the resonance plate, thereby achieving the effect of sound absorption.

[0012] According to the above technical solution, the rectifying member includes a first fairing and a second fairing. The first fairing and the second fairing are coaxially installed at the air inlet position. The diameter of the second fairing is smaller than that of the first fairing. The second fairing is located inside the first fairing. Both the first fairing and the second fairing are designed to be streamlined to reduce the impact generated when the gas enters the interior of the housing. A flow guiding member is coaxially installed inside the housing with the impeller, the air inlet, and the rectifying member;

[0013] The gas that enters the interior of the housing through the gap between the first fairing and the second fairing diffuses to both sides of the impeller and is accelerated by the centrifugal force of the impeller rotating at high speed. The gas that enters the interior of the housing through the second fairing is guided to the position of the flow guiding member to eliminate the intake vortex generated by the gas entering the interior of the housing through the air inlet, thereby reducing the noise.

[0014] According to the above technical solution, the flow guiding member includes a flow guiding seat, a flow guiding cavity, a guiding cone, and a guiding hole;

[0015] The flow guiding seat is installed inside the impeller and is used to guide the airflow that enters the interior of the housing through the second fairing, avoid generating an intake vortex, and thereby reduce the generation of noise. The flow guiding seat is provided with a flow guiding cavity on the side facing the rectifying member, so that the airflow can enter the interior of the flow guiding cavity. A guiding cone is installed inside the flow guiding cavity and is used to divide the airflow that enters the interior of the flow guiding cavity. The side wall of the flow guiding seat is provided with a guiding hole. The flow guiding cavity and the guiding cone are used to guide the airflow to the guiding hole, and the airflow is guided to the position of the impeller through the guiding hole, thereby improving the operating efficiency of the fan.

[0016] According to the above technical solution, the flow guiding member rotates synchronously with the impeller, and the guiding hole is curved along the rotation direction of the impeller. When the gas enters the flow guiding cavity, under the rotational action of the flow guiding seat, the gas flows out through the guiding hole, so that the initial flow direction of the gas is the same as the rotation direction of the impeller, thereby improving the operating efficiency of the fan. Moreover, since the guiding hole is curved along the rotation direction of the impeller, pre-whirl intake is achieved, reducing the impact of the airflow on the impeller, and thereby reducing the noise.

[0017] According to the above technical solution, the impeller is composed of a hub and blades. The blades are backward-curved blades, forming an arc convex surface and an arc concave surface. A turning portion is provided at the trailing edge of the blade. A flow guiding hole penetrating the blade is provided at the turning portion and the arc convex surface. Through the design of the flow guiding hole, when the blade rotates, part of the gas can flow through the flow guiding hole, so that there is also gas flow at the trailing edge of the arc concave surface, reducing the possibility of the occurrence of Karman vortex streets caused by the separation of the airflow boundary layer, thereby avoiding the pressure fluctuation caused by the alternating detachment of the vortices and reducing the possibility of noise generation.

[0018] According to the above technical solution, the included angle formed by the surface of the turning part and the surface of the arc convex surface is an obtuse angle. Since the drainage hole is installed at the position of the turning part and the arc convex surface, the air flow rate through the drainage hole can be further increased.

[0019] According to the above technical solution, the central axis of the end of the diversion hole is on the same axis as the central axis of the drainage hole. When the gas flows out through the diversion hole, a part of the gas will directly reach the position of the arc concave surface through the drainage hole, thereby ensuring the gas volume at the trailing edge of the arc concave surface, avoiding the generation of von Karman vortex streets due to boundary layer separation, and at the same time, the impact of the air flow on the blade can also be reduced, realizing the noise reduction treatment of the fan.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] 1. By providing the second volute tongue part and arranging the diversion members at equal intervals on the side of the second volute tongue part close to the impeller, the present invention enables the air flow accelerated by centrifugal force to be accelerated through the diversion members and the gradually decreasing diameter diversion channels formed by the diversion members when part of the air flow enters the interior of the housing, thereby reducing the speed difference between the air flow entering the housing through the volute tongue and the originally accelerated air flow inside the housing, reducing the impact between the air flows, and further reducing the noise. At the same time, through the design of the resonance cavity and the resonance plate, the vibration generated by the impact between the air flow and the volute tongue can be weakened, further reducing the noise.

[0022] 2. Through the design of the rectifying member and the drainage member, the present invention can guide the air flow entering the interior of the housing, enabling part of the air flow to be directly accelerated by the centrifugal force of the impeller, and the other part of the air flow to be accelerated by the centrifugal force of the impeller after being drained by the drainage member, eliminating the intake vortex, reducing the impact between the air flow and the impeller, thereby reducing the noise and also improving the operating efficiency of the fan.

[0023] 3. Through the bending design of the diversion hole, the present invention realizes pre-whirl intake, reduces the impact of the air flow on the impeller, thereby reducing the noise. At the same time, the central axis of the end of the diversion hole is on the same axis as the central axis of the drainage hole. When the gas flows out through the diversion hole, a part of the gas will directly reach the position of the arc concave surface through the drainage hole, thereby ensuring the gas volume at the trailing edge of the arc concave surface, avoiding the generation of von Karman vortex streets due to boundary layer separation, and at the same time, the impact of the air flow on the blade can also be reduced, realizing the noise reduction treatment of the fan. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the overall structure of a noise-reducing centrifugal ventilator structure of the present invention;

[0025] Figure 2 It is a schematic diagram of the installation structure of the impeller in a noise-reducing centrifugal ventilator structure of the present invention;

[0026] Figure 3 This is a cross-sectional view of the structure of a noise-reducing centrifugal ventilator according to the present invention;

[0027] Figure 4 This is a schematic structural diagram of the first volute tongue part and the second volute tongue part in the structure of a noise-reducing centrifugal ventilator according to the present invention;

[0028] Figure 5 This is a schematic structural diagram of the guide member in the structure of a noise-reducing centrifugal ventilator according to the present invention;

[0029] Figure 6 This is a schematic installation structure diagram of the resonance cavity and the resonance plate in the structure of a noise-reducing centrifugal ventilator according to the present invention;

[0030] Figure 7 This is a schematic installation position diagram of the rectifying member and the flow guiding member in the structure of a noise-reducing centrifugal ventilator according to the present invention;

[0031] Figure 8 This is a schematic structural diagram of the rectifying member in the structure of a noise-reducing centrifugal ventilator according to the present invention;

[0032] Figure 9 This is a schematic diagram of the air flow guiding at the air inlet in the structure of a noise-reducing centrifugal ventilator according to the present invention;

[0033] Figure 10 This is a schematic structural diagram of the flow guiding member in the structure of a noise-reducing centrifugal ventilator according to the present invention;

[0034] Figure 11 This is a cross-sectional view of the flow guiding member in the structure of a noise-reducing centrifugal ventilator according to the present invention;

[0035] Figure 12 This is a first perspective view of the blade in the structure of a noise-reducing centrifugal ventilator according to the present invention;

[0036] Figure 13 This is a second perspective view of the blade in the structure of a noise-reducing centrifugal ventilator according to the present invention.

[0037] Explanation of reference numerals:

[0038] 1. Housing;

[0039] 201. Disk; 202. Blade; 203. Arc convex surface; 204. Arc concave surface; 205. Transition part; 206. Drainage hole;

[0040] 3. Driving component; 4. Air inlet;

[0041] 501. First rectifying cover; 502. Second rectifying cover;

[0042] 6. Air outlet; 7. First volute tongue part; 8. Second volute tongue part; 9. Deflector; 10. Deflection channel; 11. Resonance cavity; 12. Resonance plate; 13. Connecting piece;

[0043] 1401. Drainage seat; 1402. Drainage cavity; 1403. Deflection cone; 1404. Deflection hole. Detailed implementation manner

[0044] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0045] Embodiment: As Figures 1 - 3 shown, the present invention provides a noise reduction type centrifugal ventilator structure, including a housing 1 and an impeller driven to rotate inside the housing 1 by a driving component 3. The driving component 3 can be a motor. The motor can be directly key-connected to the impeller or connected to the impeller through belt transmission. The distance between the inner wall of the housing 1 and the outer edge of the impeller gradually increases along the rotation direction of the impeller, aiming to prevent a large pressure gradient from being generated inside the housing 1 by the airflow, resulting in excessive noise. An air inlet 4 and an air outlet 6 are respectively provided in the axial and radial directions of the housing 1. The axially installed air inlet 4 allows external gas to enter the inside of the housing 1 and is discharged through the radially installed air outlet 6 under the action of the centrifugal force generated by the rotation of the impeller. A rectifying component for guiding the inflowing gas is provided at the position of the air inlet 4. Through the design of the rectifying component, the airflow entering the inside of the housing 1 becomes smoother. At the same time, the flow direction of the gas entering the inside of the housing 1 is guided, eliminating the intake vortex, reducing the impact between the airflow and the impeller, thereby reducing noise and improving the operating efficiency of the fan.

[0046] As Figures 4 - 6 shown, a first volute tongue part 7 is provided at the connection between the air outlet 6 and the housing 1. A second volute tongue part 8 is provided at the end of the first volute tongue part 7. The side of the second volute tongue part 8 close to the air outlet 6 is smoothly connected to the first volute tongue part 7 to prevent a sudden change in the cross-sectional area at the air outlet 6 from causing a sudden change in the flow velocity of the airflow at the air outlet 6. The second volute tongue part 8 is inclined towards the impeller side. By the second volute tongue part 8, the gap between the volute tongue and the impeller is further reduced, preventing the gas accelerated by the centrifugal force of the impeller from re-entering the housing 1 through the gap and affecting the operating efficiency of the fan.

[0047] The first volute tongue part 7 and the second volute tongue part 8 are welded to the housing 1 and then the welding points are polished to form;

[0048] A resonance cavity 11 is provided inside the first volute tongue portion 7. The cross-section of the resonance cavity 11 can be designed as a triangle, with one vertex of the triangle facing the second volute tongue portion 8. The purpose is to better transmit the vibration generated by the volute tongue, thereby achieving better vibration reduction. Inside the resonance cavity 11, a resonance plate 12 is installed along the radial direction of the housing 1 through a connecting member 13. When the gas accelerated by the centrifugal force of the impeller impacts the volute tongue, the resonance cavity 11 and the resonance plate 12 inside it vibrate, thereby canceling out the overall vibration of the volute tongue and reducing the noise generated by the airflow impacting the volute tongue at the air outlet 6.

[0049] The inside of the resonance cavity 11 is in a vacuum state. By evacuating the resonance cavity 11, the transmission of the sound generated by the vibration of the resonance plate 12 inside the resonance cavity 11 is blocked. The connecting member 13 is an elastic connecting member. For example, the resonance plate 12 and the side wall of the resonance cavity 11 are connected by an elastic rope. The purpose is also to weaken the transmission of the sound generated by the vibration of the resonance plate 12, thereby achieving the effect of sound elimination.

[0050] A number of flow guiding members 9 are arranged at equal intervals on the side of the second volute tongue portion 8 close to the impeller. A flow guiding channel 10 is formed between two adjacent flow guiding members 9.

[0051] The width of the flow guiding member 9 gradually increases along the gas flow direction, causing the flow guiding channel 10 to gradually decrease along the gas flow direction. The purpose is that when a small part of the gas re-enters the inside of the housing 1 through the gap, the flow guiding channel 10 can be used to increase the flow velocity of the gas, thereby avoiding the pressure exchange between the gas entering the inside of the housing 1 through the gap between the volute tongue and the impeller and the gas accelerated inside the housing 1, forming a periodic pulse, and achieving the function of noise reduction.

[0052] In this embodiment, the impeller is driven to rotate by a motor. The outside air enters the inside of the fan housing 1 through a rectifying member. The gas is accelerated by the centrifugal force generated during the rotation of the impeller and flows through the gap between the impeller and the housing 1 to the position of the air outlet 6 and is discharged through the air outlet 6.

[0053] As Figures 7 - 8 shown, the rectifying member includes a first rectifying cover 501 and a second rectifying cover 502. The first rectifying cover 501 and the second rectifying cover 502 are coaxially installed at the air inlet 4 position. The diameter of the second rectifying cover 502 is smaller than that of the first rectifying cover 501. The second rectifying cover 502 is located inside the first rectifying cover 501. Both the first rectifying cover 501 and the second rectifying cover 502 are designed in a streamline shape to reduce the impact generated when the gas enters the inside of the housing 1. A flow guiding member is coaxially installed inside the housing 1 with the impeller, the air inlet 4, and the rectifying member.

[0054] As Figure 9As shown, the gas that enters the interior of the housing 1 through the gap between the first fairing 501 and the second fairing 502 diffuses to both sides of the impeller and is accelerated by the centrifugal force of the high-speed rotating impeller. The gas that enters the interior of the housing 1 through the second fairing 502 is guided to the position of the flow guiding member, eliminating the intake vortex generated by the gas entering the interior of the housing 1 through the air inlet 4, thereby reducing noise.

[0055] As Figures 10 - 11 shown, the flow guiding member includes a flow guiding base 1401, a flow guiding cavity 1402, a flow guiding cone 1403, and a flow guiding hole 1404;

[0056] The flow guiding base 1401 is installed inside the impeller and is used to guide the airflow that enters the interior of the housing 1 through the second fairing 502, avoiding the generation of intake vortex, thereby reducing the generation of noise. A flow guiding cavity 1402 is provided on the side of the flow guiding base 1401 facing the rectifying member, allowing the airflow to enter the interior of the flow guiding cavity 1402. A flow guiding cone 1403 is installed inside the flow guiding cavity 1402 and is used to divide the airflow entering the interior of the flow guiding cavity 1402. Flow guiding holes 1404 are provided on the side wall of the flow guiding base 1401. The flow guiding cavity 1402 and the flow guiding cone 1403 are used to guide the airflow to the flow guiding holes 1404, and the airflow is guided to the position of the impeller through the flow guiding holes 1404, thereby improving the operating efficiency of the fan.

[0057] The flow guiding member rotates synchronously with the impeller, and the flow guiding holes 1404 are bent along the rotation direction of the impeller. When the gas enters the flow guiding cavity 1402, under the rotational action of the flow guiding base 1401, the gas flows out through the flow guiding holes 1404, making the initial flow direction of the gas the same as the rotation direction of the impeller, thereby improving the operating efficiency of the fan. Moreover, since the flow guiding holes 1404 are bent along the rotation direction of the impeller, pre-whirl intake is achieved, reducing the impact of the airflow on the impeller, thereby reducing noise.

[0058] In this embodiment, the gas that enters the interior of the housing 1 through the second fairing 502 enters the interior of the flow guiding cavity 1402 and, under the action of the flow guiding cone 1403, is dispersed into the flow guiding holes 1404. At the same time, the entire flow guiding base 1401 rotates with the rotation of the impeller, causing the gas to flow out through the flow guiding holes 1404.

[0059] As Figures 12 - 13As shown in the figure, the impeller consists of a disk 201 and blades 202. The blades 202 are backward-curved blades, forming an arc convex surface 203 and an arc concave surface 204. A turning portion 205 is provided at the trailing edge of the blade 202. A drainage hole 206 penetrating the blade 202 is provided at the position of the turning portion 205 and the arc convex surface 203. Through the design of the drainage hole 206, when the blade 202 rotates, part of the gas can flow through the drainage hole 206, so that there is also gas flow at the trailing edge of the arc concave surface 204, reducing the possibility of the formation of a Karman vortex street due to the separation of the air flow boundary layer, thus avoiding the pressure fluctuation caused by the alternating detachment of vortices and reducing the possibility of noise generation.

[0060] Among them, the trailing edge refers to the part of the arc concave surface 204 close to the guiding member.

[0061] The included angle formed by the surface of the turning portion 205 and the surface of the arc convex surface 203 is an obtuse angle. For example, the formed included angle is 135°. Since the drainage hole 206 is installed at the position of the turning portion 205 and the arc convex surface 203, the air flow rate through the drainage hole 206 can be further increased.

[0062] The central axis of the end of the diversion hole 1404 is on the same axis as the central axis of the drainage hole 206. When the gas flows out through the diversion hole 1404, part of the gas will directly reach the position of the arc concave surface 204 through the drainage hole 206, thus ensuring the gas volume at the trailing edge of the arc concave surface 204, avoiding the formation of a Karman vortex street due to boundary layer separation, and at the same time, it can also reduce the impact of the air flow on the blade 202, realizing the noise reduction treatment of the fan.

[0063] In this embodiment, the gas flowing out through the diversion hole 1404 will be accelerated under the action of the blade 202. At the same time, part of the gas flowing out through the diversion hole 1404 will flow through the drainage hole 206, and part of the gas flowing through the arc convex surface 203 will also flow through the drainage hole 206. Under this action, part of the air flow can flow through the trailing edge of the arc concave surface 204, and the formation of a Karman vortex street due to boundary layer separation can be avoided.

[0064] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, in any aspect, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention. Any reference signs in the claims should not be regarded as limiting the claims involved.

Claims

1. A noise-reducing centrifugal fan structure, comprising a housing (1) and an impeller rotatably driven by a driving component (3) inside the housing (1), wherein an air inlet (4) and an air outlet (6) are respectively formed in the axial and radial directions of the housing (1), and is characterized in that: A rectifying member for guiding the inflowing gas is provided at the position of the air inlet (4); A first volute tongue portion (7) is provided at the connection between the air outlet (6) and the housing (1). A second volute tongue portion (8) is provided at the end of the first volute tongue portion (7). The side of the second volute tongue portion (8) close to the air outlet (6) is smoothly connected to the first volute tongue portion (7). The second volute tongue portion (8) inclines towards the impeller side. A plurality of guide members (9) are provided at equal distances on the side of the second volute tongue portion (8) close to the impeller. A guide channel (10) is formed between two adjacent guide members (9); The width of the guide member (9) gradually increases along the gas flow direction, so that the guide channel (10) gradually decreases along the gas flow direction.

2. The noise-reducing centrifugal fan structure according to claim 1, wherein: A resonance cavity (11) is opened inside the first volute tongue portion (7). A resonance plate (12) is installed inside the resonance cavity (11) along the radial direction of the housing (1) through a connecting member (13).

3. The structure of a noise-reducing centrifugal ventilator according to claim 2, characterized in that: The inside of the resonance cavity (11) is in a vacuum state, and the connecting member (13) is an elastic connecting member.

4. A noise reduction type centrifugal fan structure according to claim 1, characterized in that: The rectifying member includes a first rectifying cover (501) and a second rectifying cover (502). The first rectifying cover (501) and the second rectifying cover (502) are coaxially installed at the position of the air inlet (4). The diameter of the second rectifying cover (502) is smaller than that of the first rectifying cover (501). The second rectifying cover (502) is located inside the first rectifying cover (501). A guiding member is coaxially installed inside the housing (1) with the impeller, the air inlet (4) and the rectifying member.

5. The structure of a noise-reducing centrifugal fan according to claim 4, wherein: The guiding member includes a guiding seat (1401), a guiding cavity (1402), a guiding cone (1403) and a guiding hole (1404); The guiding seat (1401) is installed inside the impeller. A guiding cavity (1402) is opened on the side of the guiding seat (1401) facing the rectifying member. A guiding cone (1403) is installed inside the guiding cavity (1402). A guiding hole (1404) is opened on the side wall of the guiding seat (1401).

6. The structure of a noise-reducing centrifugal ventilator according to claim 5, wherein: The guiding member rotates synchronously with the impeller, and the guiding hole (1404) is bent along the rotation direction of the impeller.

7. A noise reduction type centrifugal fan structure according to any one of claims 5-6, characterized in that: The impeller is composed of a wheel disc (201) and blades (202). The blades (202) are backward curved blades, forming an arc convex surface (203) and an arc concave surface (204). A turning portion (205) is provided at the trailing edge of the blade (202). A guiding hole (206) penetrating the blade (202) is opened at the turning portion (205) and the arc convex surface (203) position.

8. A noise-reducing centrifugal fan structure according to claim 7, characterized in that: The included angle formed by the surface of the turning portion (205) and the surface of the arc convex surface (203) is an obtuse angle.

9. The structure of a noise-reducing centrifugal ventilator according to claim 7, characterized in that: The central axis of the end of the guiding hole (1404) and the central axis of the guiding hole (206) are on the same axis.

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