A double-impeller centrifugal fan with a noise-reducing centrifugal impeller

Abstract

The application discloses a double-impeller centrifugal fan with a noise-reducing type centrifugal impeller, and belongs to the technical field of cooling fans. The double-impeller centrifugal fan comprises a rack, a motor and an impeller. The end of the rack is provided with an air inlet channel, and the side wall of the rack is provided with an air outlet channel. The impeller comprises a rear wheel disc, a front wheel disc and a plurality of blades. The plurality of blades are respectively in the form of arc-shaped plates and are clamped between the rear wheel disc and the front wheel disc. The plurality of blades are arranged in a circumferential rotational symmetry on the radial plane of the impeller. The air inlet of the front wheel disc is arranged opposite to the air inlet channel. The application controls the cutting angle of the air outlet end and the air inlet end of the blade within a certain angle range, ensures that the blade has a large air extraction efficiency and reduces the noise influence. The beveling design of the air outlet cutting edge and the air inlet cutting edge of the blade can improve the airflow unevenness at the turning position, thereby changing the circumferential velocity of the airflow at different sections of the blade and making the airflow at the leading edge of the blade enter the impeller flow channel as much as possible without impact.

Description

Technical Field

[0001] This invention belongs to the field of heat dissipation fan technology, specifically a dual-impeller centrifugal fan with a noise-reducing centrifugal impeller. Background Technology

[0002] With the rapid development of rail transit technology, subway, urban rail, and high-speed rail vehicles are gradually evolving towards higher speeds, higher efficiency, and environmental friendliness. During train operation, the traction motor provides the power for the train's forward movement, while the traction converter controls the starting, braking, and speed regulation of the traction motor. Especially as train speeds increase, the heat generated by the traction motor and converter increases significantly. If heat cannot be dissipated effectively and in a timely manner, it will directly affect the operational stability and service life of the equipment.

[0003] Currently, centrifugal fans are widely used to provide cooling air for traction converters and traction motors. They use high-speed rotation to send a large amount of cold air into the converter cabinet, forcibly cooling and ventilating the internal heat-generating components, and quickly carrying away the generated heat and dissipating it into the atmosphere to maintain the normal operating temperature of the equipment.

[0004] However, traditional centrifugal fans generate significant aerodynamic and mechanical noise when operating at high speeds, and are inadequate in noise control. This noise not only adversely affects the comfort of the train's interior environment but may also lead to noise pollution in the external environment, making it difficult to meet the increasingly stringent sound quality requirements for rail transit vehicles. Summary of the Invention

[0005] The purpose of this invention is to provide a dual-impeller centrifugal fan with a noise-reducing centrifugal impeller to solve the problems mentioned in the prior art.

[0006] A dual-impeller centrifugal fan with a noise-reducing impeller is provided, comprising:

[0007] A frame, wherein an air inlet is provided at one end of the frame and an air outlet is provided on the side wall of the frame opposite to the air inlet;

[0008] An electric motor, which is disposed inside the frame;

[0009] The impeller includes a rear impeller, a front impeller, and several blades. The rear impeller is fixedly connected to the output shaft of the motor. Each of the blades is held between the rear impeller and the front impeller in an arc-shaped plate shape. The blades are arranged symmetrically in a circumferential direction on the radial plane of the impeller. The air inlet of the front impeller is arranged opposite to the air inlet duct.

[0010] The blades have an air outlet located on the outer circle of the blade rotation path ring and an air inlet located on the inner circle of the blade rotation path ring on the radial plane of the impeller. The tangent of the air outlet on the outer circle of the rotation path ring and the extension of the air outlet form an angle of β1 degrees, with 30°≤β1≤60°. The tangent of the air inlet on the inner circle of the rotation path ring and the extension of the air inlet form an angle of β2 degrees, with 15°≤β2≤35°.

[0011] The side of the blade at the air outlet is the air outlet tangent, and the side of the blade at the air inlet is the air inlet tangent. The extension line of the air outlet tangent forms an angle of α1 degrees with the central axis of the impeller, where 0 < α1 ≤ 9°. The extension line of the air inlet tangent forms an angle of α2 degrees with the central axis of the impeller, where 0 < α2 ≤ 9°.

[0012] As a further aspect of the present invention: the tangent of the air outlet end on the outer circle of the rotating path ring and the extension line of the air outlet end form an angle of β1 degrees and 32°≤β1≤36°, and the tangent of the air inlet end on the inner circle of the rotating path ring and the extension line of the air inlet end form an angle of β2 degrees and 19°≤β2≤23°.

[0013] As a further aspect of the present invention: the line connecting the two endpoints of the inlet cut edge is an extension line of the inlet cut edge, and the inlet cut edge forms a continuously undulating concave-convex structure relative to the extension line. To reduce the impact vortex of the airflow at the blade leading edge and reduce the vortex noise at the impeller inlet, the inlet cut edge of the blade can be designed as an irregular concave-convex curve structure.

[0014] As a further aspect of the present invention: the line connecting the two endpoints of the outlet cut edge is an extension line of the outlet cut edge, and the outlet cut edge forms a continuously undulating concave-convex structure relative to the extension line. Similar to the structure of the inlet cut edge, the outlet cut edge of the blade can be designed as an irregular concave-convex curve structure to disperse the shedding vortices of fluid-solid separation at the blade trailing edge and reduce impeller outlet vortex noise.

[0015] As a further aspect of the invention: a plane rotating around the impeller's central axis is used as a tangent, and the part where this tangent intersects with the blade is the blade's projection plane. The extension line of this projection plane forms an angle of γ degrees with the impeller's central axis, where 0° < γ ≤ 20°. The airflow characteristic inside the impeller is that the velocity near the front impeller disk is greater than the velocity near the rear impeller disk. At this point, the axial angle between the blade and the rear impeller disk can be tilted by a certain angle γ, resulting in a larger flow area closer to the front impeller disk, reducing the airflow velocity, and minimizing vortex losses caused by airflow separation.

[0016] As a further aspect of the present invention: the air inlet duct forms a cylindrical air duct structure that first contracts inward and then expands outward along the airflow direction. The air inlet duct forms a constriction structure in the middle region, causing the airflow to accelerate first and then decelerate. This results in a very smooth airflow entering the impeller, minimizing inlet impact and vortexes, and reducing inlet vortex noise.

[0017] As a further aspect of the present invention: the air inlet end of the air inlet duct is a cone shape that gradually narrows along the airflow direction, and the contraction angle of the cone shape is φ and 40°≤φ≤60°.

[0018] As a further aspect of the present invention: the air outlet end of the air inlet duct is fitted inside the front impeller, the axial overlap between the air inlet duct and the front impeller on the impeller's central axis is h = 2mm to 6mm, and the radial gap between the air inlet duct and the front impeller on the impeller's central axis is δ = (0.5% to 1%)D. m D m This is the inner diameter of the front impeller in this radial plane. This design is used to reduce airflow leakage loss and eddies caused by leakage, thereby ensuring low impeller noise.

[0019] As a further aspect of the present invention: an air inlet duct is provided at each end of the frame, the motor has two output shafts, the number of impellers is two, the two impellers are fixedly connected to the two output shafts of the motor respectively, and the two impellers are arranged opposite to the two air inlets respectively.

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

[0021] The impeller is a backward-curved centrifugal impeller structure. Airflow enters through the inlet axially upward through the blades and exits radially. The extraction efficiency is mainly controlled by the chamfer angles of the blades' outlet and inlet ends. This invention controls the chamfer angles of the blades' outlet and inlet ends within a certain range, ensuring high extraction efficiency while reducing noise. The oblique cut design of the blade's outlet and inlet edges improves the uneven airflow at bends without changing the chamfer angles, thereby altering the circumferential velocity of the airflow at different blade cross-sections, allowing the airflow at the blade's leading edge to enter the impeller channel with minimal impact. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of this drawing or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this drawing. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0023] Figure 1 An exploded view of the overall structure of a dual-impeller centrifugal fan with a noise-reducing impeller;

[0024] Figure 2 A cross-sectional structural arrangement diagram of the blades on the radial plane of the impeller;

[0025] Figure 3 This is a schematic diagram of the impeller structure;

[0026] Figure 4 This is a schematic diagram of the blade structure;

[0027] Figure 5 Examples of blade cut edges under different concave and convex structural states;

[0028] Figure 6 This is a schematic diagram of the oblique cut structure of the blade;

[0029] Figure 7 This is a schematic diagram of the tilting structure of the blade;

[0030] Figure 8 This is a schematic diagram showing the assembly state of the air inlet and the impeller.

[0031] Figure 9 for Figure 8 A magnified view of region A in the middle.

[0032] In the diagram: 1. Frame; 11. Air inlet duct; 12. Air outlet duct; 2. Motor; 3. Impeller; 31. Rear impeller; 32. Front impeller; 33. Blade; 331. Air outlet end; 332. Air inlet end; 333. Air outlet cut edge; 334. Air inlet cut edge. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described and illustrated below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. All other embodiments obtained by those skilled in the art based on the embodiments provided by this invention without inventive effort are within the scope of protection of this invention.

[0034] Obviously, the accompanying drawings described below are merely some examples or embodiments of the present invention. Those skilled in the art can apply the present invention to other similar scenarios based on these drawings without any inventive effort. Furthermore, it is understood that although the efforts made in this development process may be complex and lengthy, for those skilled in the art related to the content disclosed in this invention, modifications to design, manufacturing, or production based on the technical content disclosed in this invention are merely conventional technical means and should not be construed as insufficient disclosure of the present invention.

[0035] However, there may be instances where unnecessary detailed descriptions are omitted. For example, detailed descriptions of well-known matters or repetitive descriptions of essentially the same structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the invention and are not intended to limit the subject matter of the claims.

[0036] Please see Figure 1 As shown in the embodiment of the present invention, a dual-impeller centrifugal fan with a noise-reducing centrifugal impeller includes a frame 1, a motor 2, and an impeller 3. An air inlet duct 11 is provided at the end of the frame 1, and an air outlet duct 12 is provided on the side wall of the frame 1 opposite to the air inlet duct 11. The motor 2 is disposed inside the frame 1. The impeller 3 includes a rear impeller 31, a front impeller 32, and several blades 33. The rear impeller 31 is fixedly connected to the output shaft of the motor 2. The several blades 33 are each arc-shaped plate sandwiched between the rear impeller 31 and the front impeller 32. The several blades 33 are symmetrically arranged circumferentially on the radial plane of the impeller 3. The air inlet of the front impeller 32 is arranged opposite to the air inlet duct 11.

[0037] Except for the air inlet duct 11 and the air outlet duct 12, the frame 1 is an enclosed structure. The motor 2 is installed inside the frame 1 and is used to drive the impeller 3 to rotate within the frame 1. When the impeller 3 rotates, the airflow enters the axial cavity area of ​​the impeller 3 from the air inlet duct 11, and is guided laterally to the impeller 3 by multiple circumferential blades 33, and finally the airflow is output from the air outlet duct 12.

[0038] Please see Figures 1-3As shown, the blades 33 form an outlet end 331 on the outer circle of the rotation path ring of the blades 33 and an inlet end 332 on the inner circle of the rotation path ring of the blades 33 on the radial plane of the impeller 3. When the impeller 3 guides the airflow, the airflow enters from the inlet duct 11 and first contacts the inlet end 332, then flows along the direction of the blades 33 and finally contacts the outlet end 331. It should be noted that the outlet end 331 and the inlet end 332 of the blades 33 are obtained by taking a certain cross section on the blades 33 by a certain radial plane of the impeller 3. This cross section can be any plane taken on the blades 33. Therefore, the outlet end 331 and the inlet end 332 on the blades 33 do not refer to a single end point, but are a collection of the end points taken by various radial planes.

[0039] The tangent line of the outlet end 331 on the outer circle of the rotation path ring forms an angle of β1 degrees with its extension, where 30°≤β1≤60°. The tangent line of the inlet end 332 on the inner circle of the rotation path ring forms an angle of β2 degrees with its extension, where 15°≤β2≤35°. This angle range is used to create a pressure difference at both ends through the inclined structure of the arc-shaped plate when the blade 33 rotates, thereby generating a certain wind pressure output and improving the vortex structure to achieve noise reduction. β1 is preferably 32°~36°, and β2 is preferably 19°~23° to achieve greater ventilation efficiency and keep noise levels below the required specifications.

[0040] Please see Figures 1-4 As shown, the side of blade 33 located at the air outlet 331 is the air outlet cut-off edge 333, and the side of blade 33 located at the air inlet 332 is the air inlet cut-off edge 334. The air outlet cut-off edge 333 is the set of air outlet ends 331 intercepted by the radial planes of the impeller 3 on blade 33, representing the extension trajectory of blade 33 on the side of air outlet end 331. Similarly, the air inlet cut-off edge 334 is the set of air inlet ends 332 intercepted by the radial planes of the impeller 3 on blade 33, representing the extension trajectory of blade 33 on the side of air inlet end 332.

[0041] The line connecting the two endpoints of the outlet cut edge 333 is the extension of the outlet cut edge 333. The extension of the outlet cut edge 333 forms an angle of α1 degrees with the central axis of the impeller 3, where 0 < α1 ≤ 9°. The line connecting the two endpoints of the inlet cut edge 334 is the extension of the inlet cut edge 334. The extension of the inlet cut edge 334 forms an angle of α2 degrees with the central axis of the impeller 3, where 0 < α2 ≤ 9°. The oblique cut structure of the inlet cut edge 334 of the blade 33 can improve the uneven airflow phenomenon at the bend.

[0042] Please see Figure 6As shown, the oblique cut of the inlet tangent 334 of the blade 33 refers to the diameter D of the central cavity of the impeller 3 (excluding the rotation path of the blade 33) near the front disk 32. 1max The diameter D at point 31 of the rear wheel is greater than the diameter of the rear wheel. 1min This alters the circumferential velocity of the airflow at different radial sections within the central cavity, allowing the airflow at the leading edge of blade 33 to enter the blade passage with minimal impact. The oblique cut of the outlet tangent 333 of blade 33 refers to the diameter D of the outer circle of the blade 33's rotation path near the front impeller 32. 2max The diameter D at point 31 of the rear wheel is smaller than the diameter D of the rear wheel. 2min .

[0043] Please see Figure 1 , Figure 4 and Figure 5 As shown, to reduce the impact vortex of the leading-edge airflow and lower the vortex noise at the impeller 3 inlet, the inlet tangent edge 334 forms a continuously undulating concave-convex structure relative to its extension line. This concave-convex structure can be designed as an irregular concave-convex curve structure, or as a triangular or rectangular sawtooth structure; no specific limitation is made here. This structure aims to disperse the detached vortices from the fluid-solid separation at the leading edge of the blade 33, thereby reducing the vortex noise at the impeller 3 inlet. Similarly, when there is less vortex, the outlet tangent edge 333 can also be designed with this concave-convex structure. The specific structure will not be detailed here, but it aims to disperse the detached vortices from the fluid-solid separation at the trailing edge of the blade 33, thereby reducing the vortex noise at the impeller 3 outlet. Furthermore, the concave-convex structure changes of adjacent blades 33 can be reversed to form a reverse pulse excitation, dispersing the concentrated frequency noise and reducing rotational noise.

[0044] Please see Figure 7 As shown, the plane rotating around the central axis of the impeller 3 is taken as the tangent. The part where this tangent intersects with the blade 33 is the projection surface of the blade 33. The extension line of this projection surface forms an angle of γ degrees with the central axis of the impeller 3, where 0° < γ ≤ 20°. The airflow characteristic inside the impeller 3 is that the velocity near the front impeller 32 is greater than the velocity of the rear impeller 31. At this time, the axial angle between the blade 33 and the rear impeller 31 can be 0° (i.e., perpendicular to the rear impeller 31), or it can be tilted at a certain angle γ, so that the flow area closer to the front impeller 32 is larger, reducing the airflow velocity and reducing the vortex losses caused by airflow separation.

[0045] The number of blades 33 is n (n in this embodiment of the invention). The blades 33 are rotationally symmetrical and evenly distributed along the circumference, forming n airflow areas. The flow area gradually increases from the inlet to the outlet, and the high-speed flowing and rotating airflow is fully diffused, ensuring a sufficiently large flow rate and pressure for the fan. At the same time, the n blades 33 are not limited to being evenly distributed among the impellers 3, but can also be distributed unequally while taking into account dynamic imbalance, so that the blades 33 do not strike the air in the same frequency band, forming concentrated noise, thereby reducing the fan rotation noise.

[0046] Please see Figure 8 and Figure 9 As shown, the air inlet 11 is an axial air intake device that smoothly guides the airflow to the impeller 3. Traditional air inlets 11 are arc-shaped, with their ends vertically inserted into the front impeller 32. The airflow gradually contracts from the outside in, without any expansion process. However, the design of the air inlet 11 in this invention takes into account both its own flow loss and the flow conditions of the outlet airflow entering the impeller 3. The air inlet 11 is designed as a conical-arc structure, that is, a cone-shaped structure that gradually contracts at the inlet end, while the outlet end 331 gradually becomes a radially expanding arc shape, and the arc is consistent with the profile of the front impeller 32. This creates an arc shape with an expanding outer end, a contracting middle end, and a further expanding end. The airflow flowing within this arc undergoes a process of first accelerating and then decelerating, resulting in a very smooth airflow entering the impeller 3 and minimizing inlet impact and vortex, thus reducing inlet vortex noise.

[0047] After the fixed air inlet 11 is assembled with the rotating impeller 3, a radial clearance δ and an axial overlap h will be formed between them. The radial clearance δ between the air inlet 11 and the front impeller 32 on the central axis of the impeller 3 is (0.5%~1%)D. m D m The inner diameter of the front impeller 32 in this radial plane is given. The axial overlap h between the air inlet duct 11 and the front impeller 32 on the central axis of the impeller 3 is 2mm to 6mm. This radial clearance δ and axial overlap h are used to ensure that the impeller 3 does not collide or interfere with the front impeller 32 when it rotates normally and vibrates slightly. At the same time, they are used to reduce airflow leakage loss and eddies caused by leakage, thereby ensuring the low noise characteristic of the impeller 3.

[0048] Please see Figure 1 As shown, another aspect of the present invention provides a dual-impeller centrifugal fan. An air inlet duct 11 is provided at each end of the frame 1. The motor 2 has two output shafts, and there are two impellers 3. The two impellers 3 are fixedly connected to the two output shafts of the motor 2, and are arranged opposite to the two air inlets 11. The motor 2 is a dual-shaft three-phase AC asynchronous motor with a variable-pole independent double-winding structure, enabling high-low speed (two / four-pole) switching. When the train is running on the main line, the motor 2 operates at a high speed of two poles. When the train enters or leaves the station, as the operating speed decreases, the train control system automatically switches the motor 2 to a low-speed four-pole state, reducing fan noise and meeting urban environmental noise requirements. The motor 2 frame is made of cast aluminum stretched frame, and the front and rear end covers are made of aluminum alloy, ensuring the motor 2 is lightweight. Wide-temperature bearings are used, offering a long service life. The motor 2 is assembled and connected to the frame 1 via feet on the frame, and the shaft extension end is fitted into the impeller 3 core, driving the impeller 3 to rotate.

[0049] The design flow rate of the dual-impeller centrifugal fan is 3.7 m³ / h. 3 / s, pressure greater than 1500Pa, motor power less than 10kW, sound pressure level noise not exceeding 86dB. Each train car is equipped with two fans, providing an air volume of 2 × 1.85m³ when operating in parallel. 3 / s, wind pressure of 1600Pa, and sound power of 100dB are provided to meet the heat dissipation requirements of the traction motor and traction converter.

[0050] The converter cooling cabinet is suspended under the train car, and the fan is installed inside the cooling cabinet, located in the middle of the entire air duct. The fan dissipates heat from the traction converter and traction motor, and its reliability is critical. When the fan is working, it draws a large amount of cold air into the converter cabinet. The cold air first passes through the air inlet ducts 11 at both ends and enters the two impellers 3 at a certain inlet airflow angle and speed. After being pressurized and diffused by the impellers 3, it is output from the air outlet duct 12 and blown towards the heat-generating components of the converter, subjecting them to forced cooling. The fan quickly carries away the heat and blows it into the atmosphere, thereby achieving the purpose of cooling the traction converter.

[0051] Example 1: Performance and noise test of a fan matched with a traditional impeller and a traditional arc-shaped air inlet.

[0052] Traditional impeller structural parameters: β1=36°, β2=21°, number of blades=9, blade inlet not obliquely cut α1=0°, outlet not obliquely cut α2=0°, blades not tilted γ=0°; Traditional air inlet duct structural parameters: flow channel gradually narrows, contraction equivalent angle φ=48°, no expansion at the rear end.

[0053] Example 2: Performance and noise test of a fan matched with a conventional impeller and a conical air inlet.

[0054] Traditional impeller structural parameters: β1=36°, β2=21°, number of blades=9, blade inlet not obliquely cut α1=0°, outlet not obliquely cut α2=0°, blades not tilted γ=0°; Conical air inlet structural parameters: the flow channel first gradually narrows, the contraction equivalent angle φ=53°, and the rear end expands.

[0055] Example 3: Performance and noise test of fan matched with noise-reducing impeller and conical air inlet.

[0056] Noise-reducing impeller structural parameters: β1=36°, β2=21°, number of blades=9, blade inlet oblique cut α1=5°, outlet no oblique cut α2=0°, blades no tilting γ=0°; Conical arc-shaped air inlet structural parameters: the flow channel first gradually narrows, the contraction equivalent angle φ=53°, and the rear end expands.

[0057] Example 4: Performance and noise test of fan matched with noise-reducing impeller and conical air inlet.

[0058] Noise-reducing impeller structural parameters: β1=36°, β2=21°, number of blades=9, blade inlet non-oblique cut α1=0°, outlet oblique cut α2=6°, blades non-tilting γ=0°; Conical arc-shaped air inlet structural parameters: the flow channel first gradually narrows, the contraction equivalent angle φ=53°, and the rear end expands.

[0059] Example 5: Performance and noise test of fan matched with noise-reducing impeller and conical air inlet.

[0060] Noise-reducing impeller structural parameters: β1=36°, β2=21°, number of blades=9, blade inlet non-oblique cut α1=0°, outlet oblique cut α2=6°, blade tilt γ=10°; Conical arc-shaped air inlet structural parameters: the flow channel first gradually narrows, the contraction equivalent angle φ=53°, and the rear end expands.

[0061] Example 6: Performance and noise test of fan matched with noise-reducing impeller and conical air inlet.

[0062] Noise-reducing impeller structural parameters: β1=36°, β2=21°, number of blades=9, blade inlet oblique cut α1=5°, outlet oblique cut α2=6°, blade tilt γ=10°; Conical arc-shaped air inlet structural parameters: the flow channel first gradually narrows, the contraction equivalent angle φ=53°, and the rear end expands.

[0063] Example 7: Performance and noise test of fan matched with noise-reducing impeller and conical air inlet.

[0064] Noise-reducing impeller structural parameters: β1=36°, β2=21°, number of blades=9, blade inlet oblique cut α1=5°, outlet oblique cut α2=6°, triangular bionic sawtooth added to the outlet, blade tilt γ=10°; Conical arc-shaped air inlet structural parameters: the flow channel first gradually narrows, the contraction equivalent angle φ=53°, and the rear end expands.

[0065] Example 8: Performance and noise test of fan matched with noise-reducing impeller and conical air inlet.

[0066] Noise-reducing impeller structural parameters: β1=36°, β2=21°, number of blades=9, blade inlet oblique cut α1=5°, outlet oblique cut α2=6°, outlet with concave-convex curve profile, blade tilt γ=10°; Conical arc-shaped air inlet structural parameters: the flow channel first gradually narrows, the contraction equivalent angle φ=53°, and the rear end expands.

[0067] Table 1 compares the performance and noise levels of traditional impellers and noise-reducing impellers under the same output flow rate.

[0068]

[0069] Note: ① The A-level sound pressure level is the fan speed at a unit flow rate (1m³ / h). 3 / min), sound pressure level at unit total pressure (1Pa); ② The pressure difference ΔPa in Example 2 is obtained by comparing with Example 1, and the pressure difference ΔPa in Examples 3 to 8 is obtained by comparing with Example 2.

[0070] It should be noted that the present invention is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments that have the same structure and perform the same effects as the technical concept within the scope of the present invention are included within the scope of the present invention. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of the present invention, are also included within the scope of the present invention.

Claims

1. A double-impeller centrifugal fan with a noise-reducing centrifugal impeller, characterized in that, include: A frame (1) is provided with an air inlet duct (11) at one end, and an air outlet duct (12) is provided on the side wall of the frame (1) on the side opposite to the air inlet duct (11). Motor (2), said motor (2) is disposed inside the frame (1); The impeller (3) includes a rear impeller (31), a front impeller (32) and several blades (33). The rear impeller (31) is fixedly connected to the output shaft of the motor (2). The several blades (33) are each held in an arc-shaped plate between the rear impeller (31) and the front impeller (32). The several blades (33) are arranged symmetrically in the radial plane of the impeller (3) along the circumferential direction. The air inlet of the front impeller (32) is arranged opposite to the air inlet duct (11). The blades (33) form an air outlet (331) on the outer circle of the rotation path ring of the blades (33) and an air inlet (332) on the radial plane of the impeller (3). The tangent of the air outlet (331) on the outer circle of the rotation path ring forms an angle of β1 degrees with the extension of the air outlet (331) and 30°≤β1≤60°. The tangent of the air inlet (332) on the inner circle of the rotation path ring forms an angle of β2 degrees with the extension of the air inlet (332) and 15°≤β2≤35°. The blade (33) is located on one side of the air outlet end (331) as the air outlet cut edge (333), and the blade (33) is located on one side of the air inlet end (332) as the air inlet cut edge (334). The extension line of the air outlet cut edge (333) forms an angle of α1 degrees with the central axis of the impeller (3) and 0 < α1 ≤ 9°. The extension line of the air inlet cut edge (334) forms an angle of α2 degrees with the central axis of the impeller (3) and 0 < α2 ≤ 9°. The air outlet of the air inlet (11) is fitted inside the front impeller (32). The overlap between the air inlet (11) and the front impeller (32) on the axial direction of the impeller (3) is h=2mm~6mm. The gap between the air inlet (11) and the front impeller (32) on the radial direction of the impeller (3) is δ=(0.5%~1%)Dm, where Dm is the inner diameter of the front impeller (32) on the radial plane.

2. A double-impeller centrifugal fan with a noise-reducing centrifugal impeller according to claim 1, characterized in that, The line connecting the two endpoints of the air inlet slit (334) is the extension line of the air inlet slit (334), and the air inlet slit (334) forms a continuously undulating concave-convex structure relative to the extension line.

3. A double-impeller centrifugal fan with a noise-reducing centrifugal impeller according to claim 1, characterized in that, The line connecting the two endpoints of the air outlet cut edge (333) is the extension line of the air outlet cut edge (333), and the air outlet cut edge (333) forms a continuously fluctuating concave-convex structure relative to the extension line.

4. A double-impeller centrifugal fan with a noise-reducing centrifugal impeller according to claim 1, characterized in that, The plane rotating around the central axis of the impeller (3) is the tangent plane. The part where the tangent plane intersects with the blade (33) is the projection plane of the blade (33). The extension line of the projection plane forms an angle of γ degrees with the central axis of the impeller (3) and 0°<γ≤20°.

5. A double-impeller centrifugal fan with a noise-reducing centrifugal impeller according to claim 1, characterized in that, The air inlet duct (11) forms a cylindrical air duct structure that first contracts inward and then expands outward along the airflow direction.

6. A double-impeller centrifugal fan with a noise-reducing centrifugal impeller according to claim 5, characterized in that, The air inlet end of the air inlet duct (11) is a cone shape that gradually narrows along the airflow direction, and the contraction angle of the cone shape is φ and 40°≤φ≤60°.

7. A double-impeller centrifugal fan with a noise-reducing centrifugal impeller according to claim 1, characterized in that, The frame (1) has an air inlet duct (11) at each end. The motor (2) has two output shafts. There are two impellers (3). The two impellers (3) are fixedly connected to the two output shafts of the motor (2) respectively. The two impellers (3) are arranged opposite to the two air inlets (11).

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