Axial flow fan with bionic blade trailing edge and working method thereof

Abstract

The present invention discloses an axial flow fan with a bionic blade trailing edge, comprising a casing, and a motor and an impeller located in the casing, wherein the impeller is installed at the output shaft of the motor, wherein the impeller has an air inlet direction at the front end and an air outlet direction at the rear end, and a double-stage composite resonator is also installed at the casing, wherein the double-stage composite resonator comprises: a primary resonator arranged around the casing and a secondary resonator arranged around the primary resonator. The present invention optimizes the structure of the casing through the double-stage composite resonator to achieve noise elimination, thereby expanding the reasonable operating range of the low-noise axial flow fan, and making the axial flow fan have the characteristics of high efficiency and low noise. The present invention also discloses a working method of the axial flow fan with a bionic blade trailing edge.

Description

Technical Field

[0001] The invention relates to an axial flow fan, in particular to an axial flow fan with a bionic blade trailing edge.

[0002] The invention relates to a working method of an axial flow fan with a bionic blade trailing edge. Background Art

[0003] Nowadays, noise pollution is increasingly a concern for people. With the improvement of people's quality of life and the mandatory implementation of noise standards by the state, more stringent requirements have been put forward for the high performance and low noise of axial flow fans. However, the noise problem of fans has always been a problem that has not been completely solved in the world, and the current progress is very limited. Studies have shown that the uneven flow of air in axial flow fans is closely related to the aerodynamic performance of the fan, especially the noise. Therefore, in-depth research on the flow conditions and aerodynamic noise inside axial flow fans has a positive and far-reaching significance for improving the aerodynamic performance of the fan and reducing the noise of the fan.

[0004] The noise of axial flow fans includes mechanical noise, electromagnetic noise and aerodynamic noise. Mechanical noise and electromagnetic noise are relatively small under normal operating conditions, while aerodynamic noise is the main part and the most difficult to control. Axial flow fan noise generally has the following characteristics: fan noise has a dipole property and is composed of broadband noise and discrete noise. Discrete frequency noise contains the fundamental frequency and harmonics of the blade passing frequency; broadband noise is mainly caused by the lift pulsation acting on the blade due to vortex shedding at the trailing edge, but any large-scale turbulence in front of the blade will produce additional lift pulsation, thereby significantly increasing the radiation of broadband noise. For multi-blade fans, discrete noise is mainly caused by the lift pulsation generated by the aerodynamic interference between the moving blades and the stationary blades, and its intensity depends to a large extent on the distance between the moving and stationary blades.

[0005] During the operation of the fan, there is a blade tip gap between the rotor and the casing of the axial flow fan. Due to the uneven pressure distribution on the blade surface, the rotating blade pressure surface and suction surface generate gap vortices in the blade tip gap area, thereby generating vortex noise. The pressure on the suction surface of the blade is relatively low, and the thickness of the boundary layer close to the suction surface is large. Existing blades have the problem of large blade trailing edge thickness, which leads to uneven airflow at the trailing edge and high turbulence. The trailing edge thickness accounts for about 80% of the wake width, which is easy to generate a wake vortex, resulting in large radiation noise.

[0006] The blade passing frequency of the discrete noise and its harmonic noise are determined by the fan speed and increase with the increase of the fan speed. When the axial flow fan is operated under multiple working conditions such as variable speed, the fan discrete frequency changes with the speed and changes within a frequency band. The noise generated by the fan has a narrow silencing bandwidth and a low sound absorption coefficient under non-design conditions. Therefore, the frequency of the existing axial flow fan casing to control noise is not adjustable or has poor adjustability, the effective sound absorption bandwidth is limited, and the noise frequency is inconvenient to adjust. It has high requirements on the structural size, which is not conducive to large-scale promotion.

[0007] Therefore, it is particularly important to propose an axial flow fan with a bionic blade trailing edge that meets the structural requirements and is suitable for operation under variable speed conditions. Summary of the invention

[0008] In order to overcome the deficiencies of the prior art, the present invention provides an axial flow fan which can effectively reduce operating noise.

[0009] The technical solution adopted by the present invention to solve the technical problem is: an axial flow fan with a bionic blade trailing edge, comprising a casing, a motor and an impeller located in the casing, the impeller is installed at the output shaft of the motor, wherein the impeller air inlet direction is the front end and the impeller air outlet direction is the rear end, and a double-stage composite resonator is also installed at the casing, the double-stage composite resonator comprises:

[0010] A primary resonator is arranged around the circumference of the casing, the primary resonator comprises a primary annular inner plate which is closely attached to the surface of the casing and arranged along the circumference of the casing, a primary annular outer plate is arranged outside the primary annular inner plate, the front ends of the primary annular inner plate and the primary annular outer plate are connected through a primary front plate, and the rear ends are connected through a primary rear plate, a gap is arranged between the primary annular inner plate and the primary annular outer plate, and a closed primary resonance cavity is formed, the primary annular inner plate is provided with a primary sound absorption hole which sequentially penetrates the primary annular inner plate and the casing and extends into the casing, and the primary resonance cavity is connected with the inside of the casing through the primary sound absorption hole;

[0011] A secondary resonator is arranged around the circumference of the primary resonator, the secondary resonator includes a secondary annular inner plate which is sleeved on the outer side of the primary annular outer plate and is arranged closely to the surface of the primary annular outer plate, the secondary annular outer plate is outer-mounted with the secondary annular inner plate, the front ends of the secondary annular inner plate and the secondary annular outer plate are connected through a secondary front plate, and the rear ends are connected through a secondary rear plate, a gap is arranged between the secondary annular inner plate and the secondary annular outer plate, and a closed secondary resonance cavity is formed, the secondary annular inner plate is provided with a secondary sound absorption hole which sequentially penetrates the secondary annular inner plate and the primary annular outer plate and extends into the primary resonance cavity, and the secondary resonance cavity is communicated with the primary resonance cavity through the secondary sound absorption hole.

[0012] The beneficial effects of the present invention are as follows: after the impeller rotates, the airflow at the top of the impeller enters the first resonance cavity and the second resonance cavity through the first sound absorption hole and the second sound absorption hole respectively, thereby improving the stability of the airflow at the top of the impeller. When the sound wave propagates through the impeller with high turbulence and the blade tip gap, the sound wave passes through the porous incident resonance cavity, and fully resonates in the resonance cavity through the two-stage composite resonator, and the noise in the cavity is consumed by continuous collision and friction to improve the sound absorption coefficient of the structure. The two-stage composite resonator optimizes the structure of the casing through the two-stage composite resonator without significantly increasing the overall volume, thereby achieving noise silencing, thereby expanding the reasonable operating range of the low-noise axial flow fan, so that the axial flow fan has the characteristics of high efficiency and low noise.

[0013] It is further configured as follows: the impeller includes a hub and blades evenly distributed along the circumference of the hub, wherein the number of blades is 6 to 8, and a bionic sawtooth structure is provided at the trailing edge of each blade, and the bionic sawtooth structure is arranged along the length direction of the trailing edge; wherein the sawtooth at the bionic sawtooth structure is an equilateral triangle, and the side length of the equilateral triangle is 0.03 to 0.07 times the length of the trailing edge of the blade. The sawtooth-shaped bionic structure is provided at the trailing edge of the blade, which effectively avoids the problem of uneven airflow and high turbulence caused by the large thickness of the trailing edge of the blade, and can control the boundary layer separation and the shedding frequency of the wake vortex in the trailing edge area of ​​the blade, reduce the noise caused by lift pulsation, and the sawtooth-shaped bionic design has a vortex breaking effect, reducing the wake loss and vortex noise of the axial flow fan.

[0014] It is further configured that: the first-stage front plate and the second-stage front plate are located on the same plane and flush with the leading edge of the blade, and the first-stage rear plate and the second-stage rear plate are located on the same plane and flush with the trailing edge of the blade. Under the condition of optimizing cost and structure, the noise range of the impeller is effectively controlled and the noise reduction effect is improved.

[0015] It is further configured as follows: the primary sound absorption holes and the secondary sound absorption holes are evenly arranged along the circumference of the casing, the number of the primary sound absorption holes is x, the number of the secondary sound absorption holes is y, and the number of the blades is z, then x≥10z, y≥10z; the primary sound absorption holes and the secondary sound absorption holes are both straight-tube structures and are arranged perpendicular to the surface of the casing; the primary sound absorption holes and the secondary sound absorption holes are not located on the same straight line and are arranged staggered with each other; the hole spacing between adjacent primary sound absorption holes is 2 to 6 times the aperture of the primary sound absorption holes, and the hole spacing between adjacent secondary sound absorption holes is 2 to 6 times the aperture of the secondary sound absorption holes. By limiting the number of sound absorption holes and blades, as well as the hole spacing and aperture of the sound absorption holes, the sound absorption structure is optimized to achieve the best noise reduction and silencing effect.

[0016] It is further set that: the first-level sound absorption hole and the second-level sound absorption hole are both sound absorption holes, and the depth of the sound absorption hole is l c , the diameter of the sound absorbing hole is d c , where the aspect ratio of depth to diameter is lc / d c , the cross-sectional area of ​​the sound-absorbing hole on the primary annular inner plate or the secondary annular inner plate is S, the area of ​​the primary annular inner plate or the secondary annular inner plate is S0, and the perforation rate is P = S / S0, then

[0017] 0.3<l c / d c <0.9;

[0018] 10%<P=S / S0<30%;

[0019] The cross-sectional area of ​​the sound absorbing hole on the first-level annular inner plate is S1, the cross-sectional area of ​​the sound absorbing hole on the second-level annular inner plate is S2, and the area of ​​the first-level annular inner plate is S 01 , the area of ​​the secondary annular inner plate is S ,2 , then (S1 / S 01 )<(S2 / S 02 ). By limiting the relationship between the aspect ratio and the perforation rate, the sound absorption structure is optimized to achieve the best noise reduction and silencing effect.

[0020] It is further configured that: a secondary sound source is also provided on the secondary annular outer plate, and the secondary sound source is a speaker. There are four speakers, and the four speakers are equally arranged along the circumference of the casing. The secondary sound source is provided at the secondary annular outer plate, and a speaker structure is adopted. The sound absorption frequency can be adjusted in a limited space. The structure increases the sound absorption coefficient of the casing by changing the diaphragm speed. Without significantly increasing the volume of the equipment, the secondary composite resonator is always in the best silencing state, thereby expanding the reasonable operating range of the low-noise axial flow fan.

[0021] It is further configured as follows: a blade tip clearance ring is sleeved on the periphery of the impeller, the blade tip clearance ring is located in the gap area between the casing and the blade tip, the blade tip clearance ring is fixed to the top of the blade and rotates with the impeller. The blade tip clearance ring is installed on the outer edge of the impeller, and the pressure difference formed by the pressure surface and the suction surface of the blade is slowed down by the blade tip clearance ring to generate reverse airflow, effectively preventing the gap vortex between the pressure surface and the suction surface of the blade, thereby reducing the vortex broadband noise.

[0022] It is further set as follows: the thickness of the blade tip clearance ring is 60% to 80% of the blade tip clearance. The relationship between the blade tip clearance ring thickness and the blade tip clearance is optimized, thereby optimizing the sound absorption structure and achieving the best noise reduction and silencing effect.

[0023] It is further configured as follows: a talcum powder layer is provided on the suction surface of the blade to reduce the surface roughness of the blade to 6.3; and a rectifier net is provided at the air outlet of the casing. The talcum powder is provided on the suction surface of the blade to effectively reduce the surface roughness of the blade, reduce the thickness of the turbulent boundary layer on the suction surface, control the separation of the boundary layer, and especially slow down the rotational stall generated at low speed. At the same time, a rectifier net is installed at the air outlet of the casing to even out the outlet velocity field, further reduce the turbulent scale, and reduce broadband noise.

[0024] In order to overcome the deficiencies of the prior art, the present invention provides an axial flow fan operating method which can effectively reduce operating noise.

[0025] The technical solution adopted by the present invention to solve the technical problem is: a working method of an axial flow fan, using the above-mentioned axial flow fan, comprising the following steps:

[0026] 1) Start the axial flow fan;

[0027] 2) Inputting a voltage that increases from small to large into the speaker so that the vibration frequency generated by the diaphragm of the speaker increases from small to large, thereby changing the resonance frequency in the resonance cavity, and further achieving resonance noise reduction.

[0028] The beneficial effect of the present invention is that when the axial flow fan is in working state, a voltage that increases from small to large is input to the speaker, so that the vibration frequency generated by the diaphragm of the speaker increases from small to large, and as the vibration frequency of the diaphragm increases, the sound absorption coefficient of the casing and the secondary annular outer plate is improved. Without significantly increasing the volume of the equipment, the secondary composite resonator is always in the best silencing state, thereby expanding the reasonable operating range of the low-noise axial flow fan. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic structural diagram of an embodiment of the present invention.

[0030] Figure 2 It is a structural schematic diagram of another viewing angle of an embodiment of the present invention.

[0031] Figure 3 for Figure 2 A partial enlarged view of .

[0032] Figure 4 It is a schematic structural diagram of an embodiment of the present invention.

[0033] Figure 5 It is a schematic structural diagram of an embodiment of the present invention.

[0034] Figure 6 It is a cross-sectional view of an embodiment of the present invention.

[0035] Figure 7 for Figure 6 A partial enlarged view of B.

[0036] Figure 8 It is a cross-sectional view from another perspective of an embodiment of the present invention.

[0037] Fig. 9 for Figure 8 A partial enlarged view of C.

[0038] Fig.10 Schematic diagram of the structure of the impeller according to the embodiment of the present invention.

[0039] Fig.11 It is a schematic structural diagram of the impeller from another perspective of an embodiment of the present invention.

[0040] Impeller 1, motor 2, casing 3, rectifier network 4, blades 11, hub 12, two-stage composite resonator 31, primary resonator 31a; secondary resonator 31b, secondary sound source 32, blade trailing edge 111, blade leading edge 112, blade tip clearance ring 113, blade suction surface 114, primary sound absorbing hole 311a, primary resonance cavity 312a, primary annular inner plate 313a, primary annular outer plate 314a, primary front plate 315a, primary rear plate 316a, secondary sound absorbing hole 311b, secondary resonance cavity 312b, secondary annular inner plate 313b, secondary annular outer plate 314b, secondary front plate 315b, secondary rear plate 316b. DETAILED DESCRIPTION

[0041] The present invention will be further described below in conjunction with the accompanying drawings:

[0042] like Figures 1 to 11As shown, this embodiment includes a housing 3, and a motor 2 and an impeller 1 located in the housing 3. The impeller 1 is installed at the output shaft of the motor 2, wherein the air inlet direction of the impeller 1 is the front end and the air outlet direction of the impeller 1 is the rear end. A double-stage composite resonator 31 is also installed at the housing 3, and the double-stage composite resonator 31 includes a primary resonator 31a arranged around the side of the housing 3 and a secondary resonator 31b arranged around the periphery of the primary resonator 31a. Among them, the primary resonator 31a includes a primary annular inner plate 313a which is closely attached to the surface of the casing 3 and arranged along the circumference of the casing 3. A primary annular outer plate 314a is arranged outside the primary annular inner plate 313a. The front ends of the primary annular inner plate 313a and the primary annular outer plate 314a are connected through a primary front plate 315a, and the rear ends are connected through a primary rear plate 316a. A gap is provided between the primary annular inner plate 313a and the primary annular outer plate 314a to form a closed primary resonance cavity 312a. A circular primary sound absorption hole 311a which passes through the primary annular inner plate 313a and the casing 3 in sequence and extends into the casing 3 is opened on the primary annular inner plate 313a. The primary resonance cavity 312a is communicated with the interior of the casing 3 through the primary sound absorption hole 311a. The secondary resonator 31b includes a secondary annular inner plate 313b which is sleeved on the outside of the primary annular outer plate 314a and is closely arranged on the surface of the primary annular outer plate 314a. The secondary annular inner plate 313b is outer-mounted with the secondary annular outer plate 314b. The front ends of the secondary annular inner plate 313b and the secondary annular outer plate 314b are connected through a secondary front plate 315b, and the rear ends are connected through a secondary rear plate 316b. A gap is provided between the secondary annular inner plate 313b and the secondary annular outer plate 314b to form a closed secondary resonance cavity 312b. The secondary annular inner plate 313b is provided with a circular secondary sound absorption hole 311b which sequentially penetrates the secondary annular inner plate 313b and the primary annular outer plate 314a and extends into the primary resonance cavity 312a. The secondary resonance cavity 312b is communicated with the primary resonance cavity 312a through the secondary sound absorption hole 311b. It should be noted that in this embodiment, the primary annular inner plate 313a and the housing 3 are the same plate, i.e., an integral structure; the primary annular outer plate 314a and the secondary annular inner plate 313b are the same plate, i.e., an integral structure. In this case, although they have two names, they are actually the same plate structure. This not only saves resources, but also simplifies the structure and facilitates installation.

[0043] The impeller 1 includes a hub 12 and blades 11 uniformly distributed along the circumference of the hub 12, wherein the number of blades 11 is 6, and a bionic sawtooth structure is provided at the trailing edge of each blade 11, and the bionic sawtooth structure is arranged along the length direction of the trailing edge. The sawtooth at the bionic sawtooth structure is an equilateral triangle, and the side length of the equilateral triangle is 0.05 times the length of the trailing edge 111 of the blade. The number of blades 11 ranges from 4 to 8, and the side length of the equilateral triangle can be 0.03 to 0.07 times the length of the trailing edge 111 of the blade. The number and length ratio of the blades 11 here can be adjusted accordingly according to the actual working environment and requirements. A sawtooth-shaped bionic structure is provided at the trailing edge 111 of the blade, which can effectively avoid the problem of uneven airflow and high turbulence caused by the large thickness of the trailing edge 111 of the blade. The boundary layer separation and the shedding frequency of the wake vortex in the trailing edge 111 area of ​​the blade can be controlled, and the noise caused by lift pulsation can be reduced. The sawtooth-shaped bionic design has a vortex breaking effect, which reduces the wake loss and vortex noise of the axial flow fan.

[0044] In this embodiment, the primary front plate 315a and the secondary front plate 315b are located on the same plane and flush with the blade leading edge 112, and the primary rear plate 316a and the secondary rear plate 316b are located on the same plane and flush with the blade trailing edge 111. As can be seen from the figure, the primary front plate 315a and the secondary front plate 315b are the same annular plate structure, and the primary rear plate 316a and the secondary rear plate 316b are also the same annular plate structure. In the axial direction of the axial flow fan, the blade leading edge 112 is an oblique line inclined along the axial direction, while the blade trailing edge 111 is a straight line substantially perpendicular to the axial direction. Therefore, the primary front plate 315a and the secondary front plate 315b mentioned here are flush with the blade leading edge 112, which means that they are flush with the front end of the blade leading edge 112, and the front end here refers to the point on the blade leading edge 112 that is farthest from the blade trailing edge 111. The primary sound absorption hole 311a and the secondary sound absorption hole 311b are both through holes used to connect the acoustic pipe, and the hole shape is optimally circular.

[0045] The primary sound absorbing holes 311a and the secondary sound absorbing holes 311b are collectively referred to as sound absorbing holes. The primary sound absorbing holes 311a and the secondary sound absorbing holes 311b are evenly arranged along the circumference of the housing 3. The number of the primary sound absorbing holes 311a is x, the number of the secondary sound absorbing holes 311b is y, and the number of the blades 11 is z, then x≥10z, y≥10z. In this embodiment, the number of the primary sound absorbing holes 311a is 200, and the number of the secondary sound absorbing holes 311b is 250. The primary sound absorbing holes 311a and the secondary sound absorbing holes 311b are both straight cylindrical structures with circular cross-sections and are arranged perpendicular to the surface of the housing 3. Among them, the primary sound absorbing holes 311a and the secondary sound absorbing holes 311b are not located on the same straight line, and are arranged in an interlaced manner. The diameter of the primary sound absorbing hole 311a and the diameter of the secondary sound absorbing hole 311b are both 6 mm, and the hole spacing between adjacent primary sound absorbing holes 311a and the hole spacing between adjacent secondary sound absorbing holes 311b are both 12 mm. In addition, the depth of each sound absorbing hole is l c , the diameter of the sound absorbing hole is d c , where the aspect ratio of depth to diameter is l c / d c The cross-sectional area of ​​the sound-absorbing holes on the primary annular inner plate 313a or the secondary annular inner plate 313b is uniformly expressed as S, the area of ​​the primary annular inner plate 313a or the secondary annular inner plate 313b is uniformly expressed as S0, and the perforation rate is P = S / S0, then

[0046] 0.3<l c / d c <0.9;

[0047] 10%<P=S / S0<30%;

[0048] The cross-sectional area of ​​the sound-absorbing hole on the primary annular inner plate 313a is S1 = 5652 mm 2 The cross-sectional area of ​​the sound-absorbing hole on the secondary annular inner plate 313b is S2 = 7065 mm 2 , the area of ​​the primary annular inner plate 313a is S 01 =50240mm 2 , the area of ​​the secondary annular inner plate 313b is S 02 =56520mm 2 , then (S1 / S 01 )<(S2 / S 02 ).

[0049] In this embodiment, a secondary sound source 32 is also provided on the secondary annular outer plate 314b. The secondary sound source 32 is a speaker. There are four speakers, which are equally divided along the circumference of the casing 3. As shown in the figure, each speaker is located at four equally divided positions of the casing 3.

[0050] The impeller 1 is also provided with a blade tip clearance ring 113 at its periphery. The blade tip clearance ring 113 is located in the gap area between the inner side wall of the casing 3 and the top of the impeller 1. The blade tip clearance ring 113 is fixed to the top of the blade 11 and rotates with the impeller 1. The thickness of the blade tip clearance ring 113 is the blade tip clearance d t 80% of the diameter of the blade tip clearance ring 113 is 34 mm. Accordingly, the radial clearance between the outer side of the blade tip clearance ring 113 and the inner side wall of the casing 3 is d te , and control the radial clearance d te is the tip clearance d t Here, the thickness of the tip clearance ring 113 can be a range of values, and is the tip clearance d t 60-80% of the total surface roughness. In addition, a talcum powder layer is provided on the suction surface 114 of the blade to reduce the surface roughness of the blade 11 to 6.3. The air outlet of the casing 3 is covered with a rectifier mesh 4. The rectifier mesh 4 is composed of a wire mesh and a mesh shed surrounding the wire mesh. The wire mesh is composed of mutually perpendicular sinusoidal wires arranged in a staggered manner, and a square mesh is formed between adjacent wires. The wire mesh is welded to the inside of the annular mesh shed. The rectifier mesh 4 and the casing 3 are connected by rivets, and 3 rivets are evenly arranged along the circumference for permanent fixation. The motor 2 is a three-phase asynchronous motor, and the motor 2 is fixed to the inside of the casing 3 by a support frame.

[0051] This embodiment adopts a double-stage composite resonator 31 based on the Helmholtz resonance sound absorption principle to improve the stability of the airflow at the top of the impeller 1. t When the sound wave passes through the double-stage composite resonator 31, it fully resonates in the resonance cavity, and the noise in the cavity is consumed by continuous collision and friction, so as to improve the sound absorption coefficient of the structure.

[0052] A secondary sound source 32 is arranged on the outer wall of the double-stage composite resonator 31, and a speaker structure is adopted. The speaker is connected to the control device of the axial flow fan, and a closed feedback adjustment system is added. The sound absorption frequency can be adjusted in a limited space. The structure improves the sound absorption coefficient of the housing 3 by changing the diaphragm speed. It can be used on a variable speed fan without significantly increasing the volume of the equipment, so that the double-stage composite resonator 31 with adjustable frequency and noise reduction is always in the best silencing state, expanding the reasonable operating range of the low-noise axial flow fan. When the airflow in the axial flow fan passes through the impeller 1, the internal turbulence is large, and the sound wave enters the first-stage resonance cavity 312a. After sufficient friction and impact, the remaining part of the unconsumed sound wave enters the second-stage resonance cavity 312b through the second-stage sound absorption hole 311b. The remaining sound wave experiences cyclic friction and impact on the cavity wall again in the second-stage resonance cavity 312b, so that each stage of the resonance cavity achieves sufficient silencing.

[0053] According to the dual-microphone method, the sound absorption coefficient of the active adjustable noise reduction resonance cavity is obtained. After the two microphones collect the signal in the pipeline, the sound absorption coefficient is used as the control objective function, and the optimal amplitude and phase information required by the secondary sound source 32 in the active adjustable frequency resonance cavity is obtained through analysis to achieve the maximum sound absorption coefficient, that is, the maximum noise reduction control. The effective noise reduction bandwidth of the actively adjusted secondary resonance cavity 312b is expanded, including low-frequency, medium-frequency and high-frequency noise.

[0054] A one-dimensional sound propagation equation is established and solved along the cavity depth in the secondary resonant cavity 312b, and the impedance characteristic is obtained as follows:

[0055]

[0056] Among them, p e is the acoustic pressure on the resonant cavity surface, S is the cross-sectional area of ​​the resonant cavity, is the wave number, is the angular frequency, c is the speed of sound, Z c is the acoustic impedance of the inner wall of the secondary perforated plate. Let v a = 0, then equation (1) degenerates into the result of the traditional Helmholtz resonator:

[0057] Z P =Z c -icotkL (2)

[0058] Theoretical formula (1) shows that by adjusting the vibration speed of the loudspeaker diaphragm, the impedance characteristics of the active frequency-adjustable noise reduction resonance cavity at the snail tongue are dynamically changed, and its resonance frequency is changed to achieve the purpose of resonance noise reduction.

[0059] When the axial flow fan changes its operating conditions, the frequency of the noise radiated by the axial flow fan changes, and the speaker in the two-stage composite resonator 31 makes corresponding feedback, adjusting the vibration speed of the diaphragm to change the resonant frequency of the resonance cavity. The resonant frequency of the resonance cavity can only match the frequency of the sound waves in the incident cavity. Therefore, the sound absorption and noise reduction effect of the axial flow fan is always in the best state.

[0060] The working method of this embodiment includes the following steps:

[0061] 1) Start the axial flow fan;

[0062] 2) Inputting a voltage from small to large to the speaker so that the vibration frequency of the diaphragm of the speaker increases from small to large, thereby changing the resonance frequency in the resonance cavity until the working noise is reduced.

[0063] In the laboratory environment, the speed of the traditional axial flow fan is 810r / min and the flow rate is 915m 3 / h, the noise level is about 55dB(A); while the axial flow fan of this embodiment, when the speed is 805r / min and the flow rate is 908m 3 / h, the noise level is about 44-49dB(A). The fluctuation of the noise level is because the noise reduction effect will fluctuate at different frequencies when the secondary sound source 32 is working. At the same time, after a large number of comparative experiments in the laboratory, it is found that the effective noise reduction of this embodiment reaches 10.9-20% compared with the traditional axial flow fan, which greatly improves the working environment of the axial flow fan.

Claims

1. An axial flow fan with a bionic blade trailing edge, comprising a housing, a motor and an impeller located in the housing, wherein the impeller is mounted on the output shaft of the motor, wherein: The impeller The air inlet direction is the front end, and the impeller outlet direction is the rear end. A double-stage composite resonator is also installed at the casing, and the double-stage composite resonator includes: A primary resonator is arranged around the circumference of the casing, the primary resonator comprises a primary annular inner plate which is closely attached to the surface of the casing and arranged along the circumference of the casing, a primary annular outer plate is arranged outside the primary annular inner plate, the front ends of the primary annular inner plate and the primary annular outer plate are connected through a primary front plate, and the rear ends are connected through a primary rear plate, a gap is arranged between the primary annular inner plate and the primary annular outer plate, and a closed primary resonance cavity is formed, the primary annular inner plate is provided with a primary sound absorption hole which sequentially penetrates the primary annular inner plate and the casing and extends into the casing, and the primary resonance cavity is connected with the inside of the casing through the primary sound absorption hole; A secondary resonator is arranged around the circumference of the primary resonator, the secondary resonator includes a secondary annular inner plate which is sleeved on the outer side of the primary annular outer plate and is arranged closely to the surface of the primary annular outer plate, the secondary annular outer plate is sleeved on the secondary annular inner plate, the front ends of the secondary annular inner plate and the secondary annular outer plate are connected through a secondary front plate, and the rear ends are connected through a secondary rear plate, a gap is arranged between the secondary annular inner plate and the secondary annular outer plate, and a closed secondary resonance cavity is formed, the secondary annular inner plate is provided with a secondary sound absorption hole which sequentially penetrates the secondary annular inner plate and the primary annular outer plate and extends into the primary resonance cavity, and the secondary resonance cavity is connected with the primary resonance cavity through the secondary sound absorption hole; The primary sound absorbing holes and the secondary sound absorbing holes are evenly arranged along the circumference of the casing, the number of the primary sound absorbing holes is x, the number of the secondary sound absorbing holes is y, the number of the blades is z, then x≥10z, y≥10z; the primary sound absorbing holes and the secondary sound absorbing holes are both straight-cylindrical structures and are arranged perpendicular to the surface of the casing; the primary sound absorbing holes and the secondary sound absorbing holes are not located on the same straight line and are arranged staggered with each other; The hole spacing between adjacent primary sound absorbing holes is 2 to 6 times the aperture of the primary sound absorbing holes, and the hole spacing between adjacent secondary sound absorbing holes is 2 to 6 times the aperture of the secondary sound absorbing holes.

2. The axial flow fan with bionic blade trailing edge according to claim 1 is characterized in that: The impeller includes a hub and blades evenly distributed along the circumference of the hub, wherein the number of blades is 4 to 8, and a bionic sawtooth structure is provided at the trailing edge of each blade, and the bionic sawtooth structure is arranged along the length direction of the trailing edge; wherein the sawtooth at the bionic sawtooth structure is an equilateral triangle, and the side length of the equilateral triangle is 0.03 to 0.07 times the length of the trailing edge of the blade.

3. The axial flow fan with bionic blade trailing edge according to claim 2 is characterized in that: The primary front plate and the secondary front plate are located on the same plane and flush with the leading edge of the blade, and the primary rear plate and the secondary rear plate are located on the same plane and flush with the trailing edge of the blade.

4. The axial flow fan with bionic blade trailing edge according to claim 1, characterized in that: The first-level sound absorption hole and the second-level sound absorption hole are both sound absorption holes, and the depth of the sound absorption hole is l c , the diameter of the sound absorbing hole is d c , where the aspect ratio of depth to diameter is l c / d c , the cross-sectional area of ​​the sound-absorbing hole on the primary annular inner plate or the secondary annular inner plate is S, the area of ​​the primary annular inner plate or the secondary annular inner plate is S0, and the perforation rate is P=S / S0, then ； ； The cross-sectional area of ​​the sound absorbing hole on the first-level annular inner plate is S1, the cross-sectional area of ​​the sound absorbing hole on the second-level annular inner plate is S2, and the area of ​​the first-level annular inner plate is S 01 , the area of ​​the secondary annular inner plate is S 02 , then (S1 / S 01 )<(S2 / S 02 ).

5. The axial flow fan with bionic blade trailing edge according to claim 1, characterized in that: The secondary annular outer plate is also provided with a secondary sound source, which is a speaker. There are four speakers, which are equally spaced along the circumference of the casing.

6. The axial flow fan with bionic blade trailing edge according to claim 1, characterized in that: A blade tip clearance ring is also sleeved on the periphery of the impeller. The blade tip clearance ring is located in the gap area between the casing and the blade tip. The blade tip clearance ring is fixed to the top of the blade and rotates with the impeller.

7. The axial flow fan with bionic blade trailing edge according to claim 6, characterized in that: The thickness of the blade tip clearance ring is 60% to 80% of the blade tip clearance.

8. The axial flow fan with bionic blade trailing edge according to claim 1, characterized in that: The suction surface of the blade is covered with a talcum powder layer to reduce the surface roughness of the blade to 6.3; the air outlet of the casing is covered with a rectifier net.

9. A method for operating an axial flow fan, characterized in that: The axial flow fan according to claim 6 comprises the following steps: 1) Start the axial flow fan; 2) Inputting a voltage from small to large to the speaker so that the vibration frequency of the diaphragm of the speaker increases from small to large, thereby changing the resonance frequency in the resonance cavity until the working noise is reduced.

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