CN114233662B - Axial flow fan blade structure, axial flow fan and preparation method of axial flow fan - Google Patents

Abstract

The application discloses an axial flow fan blade structure, an axial flow fan and a preparation method thereof, wherein a concave structure is arranged on the outer edge of the axial flow fan, so that the blade top clearance of a region with strong interaction between a blade and an air guide ring is increased, the blade top clearance of a region with weak interaction is reduced, the internal flow field is improved under the condition of maintaining the area and the air quantity of the fan blade unchanged, the flowing state of air flow in the middle of the outer edge of the blade after flowing through the suction surface of the blade is improved, the leakage vortex of the blade top in the region is effectively controlled, and the turbulent kinetic energy intensity near the blade top is reduced; meanwhile, the tail air flow at the outer edge of the blade falls off and is far away from the suction surface of the blade, the local pressure pulsation on the surface of the blade is improved, the turbulence energy intensity of an internal flow field is reduced by controlling the direction of the leakage vortex at the blade top at the clearance of the blade top and the falling vortex at the tail edge, the pressure pulsation on the surfaces of the blade and the wind guide ring is weakened, and the noise of a fan is effectively improved.

Description

Axial flow blade structure, axial flow fan and preparation method thereof

Technical field

The present invention relates to the technical field of fans, specifically an axial flow fan blade structure, an axial flow fan and a preparation method thereof.

Background technique

As a traditional fluid machine, axial flow fans are widely used in factory ventilation, mine ventilation, household appliances, etc. With the current social environmental protection requirements and the continuous improvement of people's quality of life, the noise problem of axial flow fans has attracted the attention of more and more designers and developers.

The noise of air conditioning equipment mainly consists of vibration noise, aerodynamic noise, electromagnetic noise, etc., among which the aerodynamic noise of the axial flow fan used in the outdoor unit accounts for a large proportion. The aerodynamic noise of axial flow fans is mainly caused by the fluid acting on rotating blades and stationary parts such as air guide rings and other structures. In the blade top area, due to the interaction between the outer edge of the blade and the air guide ring, the airflow periodically impacts the air guide ring, causing fan rotation noise. At the same time, due to the pressure difference between the pressure surface and the suction surface of the blade, the airflow rolls from the pressure surface to the suction surface at the outer edge of the blade to form a tip leakage vortex, making the vortex noise in this area larger. In addition, the blade attack angle design, wheel hub design, etc. will also have a certain impact on the noise of the axial flow fan.

Controlling the fan rotation noise by reducing the fan speed is a common noise control method, but this method has an impact on the fan air volume performance; adding sound insulation cotton inside the air conditioner can improve the noise performance to a certain extent, but it will increase the product cost; adjust the outer edge of the fan blades The tip clearance with the air guide ring can effectively control the tip leakage vortex, but it will affect the overall performance of the fan, and this method requires high processing accuracy. Therefore, it is necessary to further improve the axial flow fan blades, so as to improve the flow state at the top of the axial flow fan blades, inhibit the development of eddy currents inside the fan, and reduce the fan noise. It is necessary to provide a new fan blade structure.

Contents of the invention

The purpose of the present invention is to provide an axial flow blade structure, an axial flow fan and a preparation method thereof to overcome the shortcomings of the existing technology. The present application can control the interaction between the blade and the air guide ring at the blade tip, and suppress the leakage of the blade tip. The development of vortex improves the aerodynamic performance of the fan and reduces the noise of the fan.

An axial flow fan blade structure includes a blade body. The outer edge curve of the blade body is a characteristic curve S0, and the characteristic curve S0 is a concave curve. The two ends of the outer edge curve of the blade body are respectively the leading edge points of the outer edge of the axial flow fan blade. A and the trailing edge point B on the outer edge of the axial flow blade. The two ends of the characteristic curve S0 coincide with the leading edge point A on the outer edge of the axial flow blade and the trailing edge point B on the outer edge of the axial flow blade respectively. The outer edge of the axial flow blade The leading edge point A is the intersection point of the blade leading edge line and the circle R=R2, the trailing edge point B is the intersection point of the blade trailing edge line and the circle R=R2, and the circle R=R2 is the radius of the axial flow fan blade with a uniform outer edge and no depression.

Furthermore, the characteristic curve S0 is the outer edge profile of the imitation butterfly wing.

Further, taking the line connecting the leading edge point A on the outer edge of the axial flow blade and the trailing edge point B on the outer edge of the axial flow blade as the x direction, and perpendicular to the connecting line as the y direction, the characteristic curve S0 equation is:

Among them, k is a non-zero real number.

Further, R2/R3=0.96-0.98, R3 is the radius of the air guide circle.

Furthermore, the difference between the maximum radius and the minimum radius of the outer edge of the axial flow blade is t, and the range of t/R3 is 0.01 to 0.05.

An axial flow fan includes a blade hub, a blade body and an air guide ring. The circumferential array of the blade body is fixed on the outer ring of the blade hub. The air guide ring is sleeved on the outer ring of the blade body. The axis of the blade hub rotates with the blade body. The center lines of the shaft and the air guide ring coincide with each other, and the end of the air guide ring is connected to the fan shell.

Further, the air guide circle includes a circular arc section, a vertical section and an outlet section connected in sequence. The circular arc section has a tapered structure, and one end of the vertical section is connected to the minimum arc radius end of the circular arc section.

A method for preparing an axial flow fan blade structure, including the following steps:

S1, based on the outer edge profile data of the butterfly wing, equation fitting is used to establish the outer edge profile of the imitation butterfly wing;

S2, take the direction of the line connecting the leading edge point and the trailing edge point of the outer edge of the butterfly wing as the x direction, and the vertical direction of the connection as the y direction, form the outer edge profile equation of the imitation butterfly wing, and scale the outer edge profile of the imitation butterfly wing as a whole Make its two end points coincide with the leading edge point of the outer edge of the axial flow blade and the trailing edge point of the outer edge of the axial flow blade respectively. The outer edge curve of the blade body is obtained as the characteristic curve. The characteristic curve is formed according to the outer edge curve of the blade body. Axial flow fan blade structure.

Furthermore, the equation of the outer edge of the imitation butterfly wing is:

Among them, k is a non-zero real number.

Further, the leading edge point A of the outer edge of the axial flow blade is the intersection point of the blade leading edge line and the circle R=R2, the trailing edge point B is the intersection point of the blade trailing edge line and the circle R=R2, and the circle R=R2 is the uniform outer edge. The radius of the concave axial flow fan blade satisfies the relationship R2/R3=0.96-0.98, R3 is the radius of the air guide ring, the difference between the maximum radius and the minimum radius of the outer edge of the axial flow fan blade is t, and the range of t/R3 is 0.01~0.05.

Compared with the existing technology, the present invention has the following beneficial technical effects:

The present invention is an axial flow fan blade structure. By arranging a recessed structure on the outer edge of the axial flow fan, the blade tip gap is increased in the area where the interaction between the blade and the air guide ring is strong, and the blade top gap is reduced in the area where the interaction is weak. , improve the internal flow field while maintaining the blade area and air volume, so that the flow state of the airflow in the middle of the blade outer edge after flowing through the blade suction surface is improved, effectively controlling the blade tip leakage vortex in this area, and reducing the blade tip The nearby turbulent kinetic energy intensity; at the same time, the airflow at the outer edge of the blade is shed away from the blade suction surface, thereby improving the local pressure pulsation on the blade surface.

Furthermore, the front and rear convex features of the characteristic curve make up for the blade area in the concave area, so that the overall work area of the blade remains unchanged.

The invention is an axial flow fan. The circumferential array of the blade body is fixed on the outer ring of the blade hub. The air guide ring is sleeved on the outer ring of the blade body. The axis of the blade hub coincides with the rotation axis of the blade body and the center line of the air guide ring. The end of the wind ring is connected to the fan casing. The recess near the middle of the outer edge of the blade increases the local blade tip gap, which weakens the interaction between the blade and the wind guide ring. By controlling the tip leakage vortex and tail at the blade tip gap, The direction of shedding vortices at the edge reduces the turbulent kinetic energy intensity of the internal flow field, weakens the pressure pulsation on the surface of blades and air guide rings, and effectively improves fan noise.

Description of the drawings

Figure 1 is a data fitting diagram of the butterfly-like airfoil line in the example of the present invention.

Figure 2 is an outline view of the butterfly-wing axial flow fan blade described in the example of the present invention.

Figure 3 is a partial outline view of the butterfly-wing axial flow fan blade in the example of the present invention.

Figure 4 is a schematic structural diagram of the butterfly wing axial flow fan blade in the example of the present invention.

Figure 5 is a structural front view of the butterfly wing axial flow fan blade in the example of the present invention.

Figure 6 is a structural left view of the butterfly wing axial flow fan blade in the example of the present invention.

Figure 7 is a schematic structural diagram of the butterfly wing axial flow fan described in the example of the present invention.

Figure 8 is a structural diagram of an outdoor unit of an air conditioner using imitated butterfly wing axial flow blades of the present invention in an embodiment of the present invention.

a in Figure 9 is a schematic diagram of the annular static pressure distribution of the air conditioner outdoor unit using the imitation butterfly wing axial flow blades of the present invention at a position 2 mm away from the air guide ring at the blade top gap of the comparative prototype and b in Figure 9 .

a in Figure 10 is a cloud diagram of turbulent kinetic energy distribution at 50% of the blade height section of the air conditioner outdoor unit using the butterfly wing axial flow blades of the present invention for a comparative prototype and b in Figure 10 .

a in Figure 11 is a schematic diagram of the mean value of the sound pressure pulsation distributed on the surface of the air-conditioning outdoor unit fan blade using the butterfly wing axial flow fan blade of the present invention for a comparison prototype and b in Figure 11 .

The comparison prototype in a in Figure 12 and the b in Figure 12 are schematic diagrams of the average sound pressure pulsation on the surface of the air guide ring of the air conditioner outdoor unit using the butterfly wing axial flow fan blades of the present invention.

Figure 13 is a comparison chart of the sound pressure level spectrum of an air conditioner outdoor unit using butterfly-wing axial flow blades of the present invention.

In the figure, 1100—blade hub; 1200—blade body; 1210—blade leading edge; 1220—blade trailing edge; 1230—blade outer edge; 1231—front convex feature; 1232—rear convex feature; 1300— Blade shaft hole; 1400—air guide ring; 1410—arc section; 1420—vertical section; 1430—exit section.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings:

As shown in Figure 2, an axial flow blade structure includes a blade body. The outer edge curve of the blade body is the characteristic curve S0. The two ends of the outer edge curve of the blade body are respectively the leading edge point A and the outer edge of the axial flow blade. The axial flow blade outer edge trailing edge point B, the line connecting the axial flow blade outer edge leading edge point A and the axial flow blade outer edge trailing edge point B is the x direction, and the line perpendicular to the connecting line is the y direction, the characteristic curve S0 The equation is:

Among them, k is a non-zero real number used to control the bionic outer edge range.

The leading edge point A of the outer edge of the axial flow blade is the intersection point of the blade leading edge line and the circle R=R2, and the trailing edge point B is the intersection point of the blade trailing edge line and the circle R=R2. Circle R=R2 is the radius of the axial flow fan blade with a uniform outer edge and no depression.

As shown in Figures 1 and 3, this application optimizes the outer edge of the blade body and obtains the outer edge curve. The two ends of the outer edge curve are respectively the leading edge point A of the outer edge of the axial flow blade and the outer edge tail of the axial flow blade. Edge point B, a concave distribution point C is set between the leading edge point A of the outer edge of the axial flow blade and the trailing edge point B of the outer edge of the axial flow blade. The ACB curve is the blade outer edge characteristic curve S0. The characteristic curve S0 is concave toward the inside of the blade at point C, forming a convex characteristic curve AC on the front side and a convex characteristic curve CB on the rear side. Their shapes are obtained by deforming the outer edge of the imitation butterfly wing.

Take the two end points of the imitation butterfly airfoil line as points a and b respectively, and the concave point in the middle of the imitation butterfly airfoil line as c.

This application adopts the outer edge structure of the imitation butterfly wing. By extracting the outer edge contour data of the silk butterfly wing, the equation is used to fit the outer edge profile of the imitation butterfly wing. The direction of the line connecting the leading edge point and the trailing edge point of the outer edge of the butterfly wing is In the x direction, the vertical direction of the connecting line is the y direction, and the equation of the outer edge of the imitation butterfly wing is:

Among them, k is a non-zero real number.

The overall shape of the butterfly wing is close to a triangle, while the outside of the axial flow blade is closer to an arc, so the outer edge of the butterfly wing needs to be deformed. Scale the outer edge of the imitation butterfly wing as a whole so that the two end points a and b coincide with the leading edge point A of the axial flow blade outer edge and the trailing edge point B of the axial flow blade outer edge respectively, so that the inner circle of the arc AB is aligned with the circle R=R1 is tangent to the outer ring, and the circle R=R1 is used to control the relative position of the butterfly airfoil line baseline. When R1 takes the minimum value, AB is a straight line; when R1 takes the maximum value, the arc AB falls on the circle R=R2. R2 is the radius of the axial flow fan blade with a uniform outer edge and no depression, which is the maximum radius of the outer edge of the blade, satisfying the relationship R2/R3 = 0.96-0.98, and R3 is the radius of the air guide ring.

Bend and deform the butterfly airfoil line chord ab and coincide with the arc AB. Each point of the profile deforms with the chord line, so that the distance from each point on the curve ACB to the arc AB is equal to the distance from each point on the curve acb to the chord line ab. The distance is consistent to create a butterfly-like outer edge of the blade. Adjust the parameter k so that when R1 takes the maximum value, the curve ACB is tangent to the circle R=R3. The difference between the maximum radius and the minimum radius of the outer edge of the axial flow blade is t, and the range of t/R3 is 0.01 to 0.05.

By arranging a concave and convex structure imitating a butterfly wing on the outer edge of the axial flow fan, the blade tip gap is increased in the area where the interaction between the blade and the air guide ring is strong, and the blade tip gap is reduced in the area where the interaction is weak. While maintaining the blade area, Improve the internal flow field while maintaining the same air volume. This design improves the flow state of the airflow in the middle of the blade outer edge after passing through the blade suction surface, effectively controls the blade tip leakage vortex in this area, and reduces the turbulent kinetic energy intensity near the blade tip; at the same time, the airflow at the rear of the blade outer edge is shed Stay away from the blade suction surface to improve local pressure pulsation on the blade surface. The front and rear convex features make up for the blade area in the concave area, keeping the overall work area of the blade unchanged.

An axial flow fan includes a blade hub 1100, a blade body 1200 and an air guide ring 1400. The blade body 1200 circumferential array is fixed on the outer ring of the blade hub 1100, and the air guide ring 1400 is sleeved on the outer ring of the blade body 1200. The axis of the blade hub 1100 coincides with the rotation axis of the blade body 1200 and the center line of the air guide ring 1400. The end of the air guide ring 1400 is connected to the fan shell. The air guide ring includes arc segments 1410, vertical segments 1420 and 1420 connected in sequence. The exit section 1430 and the arc section 1410 have a tapered structure, and one end of the vertical section 1420 is connected to the minimum arc radius end of the arc section 1410. By controlling the direction of the tip leakage vortex at the tip gap and the shedding vortex at the trailing edge, the intensity of the turbulent kinetic energy of the internal flow field is reduced, the pressure pulsation on the surface of the blade and air guide ring is weakened, and the fan noise is effectively improved.

The giant silk butterfly of the genus Silica in the family Meloididae has the habit of long-distance migration. Its maximum flight distance in a single day can reach 200km, and it has strong flight ability. During flight, the silk butterfly's wings flapping frequency is low, and it mainly relies on its shape and structural characteristics to effectively utilize sea surface airflow to glide. Since the flight speed of the giant silk butterfly is in the same order of magnitude as the inlet airflow speed of the axial flow fan for air conditioning, the concave structural features of the outer edge of the butterfly's wings can be extracted through bionic research, reconstructed and optimized, and then applied to the axial flow fan blades Designed to adjust the flow state near the top of the fan blades.

By arranging a concave and convex structure imitating a butterfly wing on the outer edge of the axial flow fan, the blade tip gap is increased in the area where the interaction between the blade and the air guide ring is strong, and the blade tip gap is reduced in the area where the interaction is weak. While maintaining the blade area, Improve the internal flow field while maintaining the same air volume. This design improves the flow state of the airflow in the middle of the blade outer edge after passing through the blade suction surface, effectively controls the blade tip leakage vortex in this area, and reduces the turbulent kinetic energy intensity near the blade tip; at the same time, the airflow at the rear of the blade outer edge is shed Stay away from the blade suction surface to improve local pressure pulsation on the blade surface. The front and rear convex features make up for the blade area in the concave area, keeping the overall work area of the blade unchanged.

By controlling the direction of the tip leakage vortex at the tip gap and the shedding vortex at the trailing edge, the intensity of the turbulent kinetic energy of the internal flow field is reduced, the pressure pulsation on the surface of the blade and air guide ring is weakened, and the fan noise is effectively improved.

Example:

As shown in Figures 2 to 7, the axial flow blade structure includes a blade hub 1100, an axial blade 1200 and a blade shaft hole 1300. The center lines of the blade hub and blade shaft holes coincide with the rotation axis of the axial flow blade. The axial flow blades are evenly connected in the circumferential direction of the hub. The three edges of the axial flow blades are the blade leading edge 1210, the blade trailing edge 1220, and the blade outer edge 1230. The existence of concave features on the outer edge of the blade divides the outer edge into a front convex feature 1231 and a rear convex feature 1232.

As shown in Figure 7, an axial flow fan includes a blade hub 1100, axial flow blades 1200, and an air guide ring 1400. The air guide circle includes an arc section 1410, a vertical section 1420, and an outlet section 1430. The arc segment 1410 extends inward along the arc line with a reduced radius and is connected to the vertical segment 1420. The vertical segment 1420 extends vertically backward to the exit segment 1430. The center lines of the impeller hub and air guide ring coincide with the rotation axis of the axial flow blades.

The airflow is collected through the air guide ring 1400 and enters the blade rotation area through the arc section 1410. After impacting the blade leading edge 1210, it passes through the blade suction surface and pressure surface along the upper and lower sides. At the blade tip position, part of the airflow turns from the pressure surface to the suction surface after passing through the convex feature 1231 on the front side, and the impact inhibits the development of shedding vortices on the suction surface there. The concavity near the middle of the outer edge of the blade increases the local blade tip gap and weakens the interaction between the blade and the wind guide ring there.

An air-conditioning outdoor unit comparison prototype was selected, and its internal axial flow fan structural parameters are shown in Table 1. A comparison group was established based on the embodiment of the comparison prototype structure equipped with imitation butterfly wing axial flow fan blades. In this embodiment, the difference t between the maximum radius and the minimum radius of the outer edge of the blade is selected to be 0.021. The comparative prototype and the embodiment are identical except for the outer edge features of the axial flow blades.

CFD software is used to establish a full three-dimensional fluid domain model. According to the outdoor unit air duct system, the fluid domain is divided into the inlet extension area, the inlet box area, the heat exchanger area, the box main area, the impeller rotation area, the outlet grille area, and the outlet. The seven parts of the extension area are shown in Figure 8. In order to control the boundary condition settings, the inlet and outlet extension areas extend upstream and downstream respectively by twice the characteristic length. The calculation domain was divided into non-structural grids. In order to ensure the accuracy and effectiveness of the numerical calculation, the grids were verified for irrelevance. The number of grids in the impeller area was finally selected to be 4.53 million, and the total number of grids was 10.74 million.

Table 1 Comparison of prototype structural parameters

Impeller diameter/mm 407 Wind circle diameter/mm 416 Impeller height/mm 131 Wind circle height/mm 70 Hub diameter/mm 90 Leaf distribution pattern Evenly distributed Hub height/mm 50 Number of leaves 3

ANSYS Fluent software was used to numerically calculate the internal flow field of the fan. The control equation was the Navier-Stokes equation, the turbulence calculation used the Realizable ke model, the near-wall equation used the standard wall function, the pressure-velocity coupling used the SIMPLE algorithm, and the pressure discretization format used PRESTO! Format, the momentum equation, energy equation and turbulence dissipation equation all adopt the second-order upwind format, and the calculation convergence residual is set to 10 ^-4 . Pressure boundary conditions are given at both the inlet and outlet, the total pressure at the inlet is set to 1 atmosphere, and the static pressure at the outlet is set to 1 atmosphere. The impeller area is set as the rotating area, the steady calculation adopts the FrameMotion model, and the rotational speed of the rotating area is set to 954 rpm. Use the steady calculation results as the initial value to perform unsteady calculations, set the time step to 0.0001s, rotate the impeller for 10 cycles, and monitor the static pressure on the wall of the air guide ring and the inlet and outlet flow rates to stabilize, and judge the calculation convergence. The FW-H equation is solved on the basis of unsteady convergence to calculate aerodynamic noise. Structural walls such as impellers, motors, wind guides, and grilles are used as noise sources, and monitoring and receiving points are set up in accordance with national standards.

The annular static pressure distribution of the comparative prototype and the embodiment of the present invention at a position 2 mm away from the air guide ring at the blade tip clearance is shown in a in Figure 9 and b in Figure 9 . It can be seen from a in Figure 9 and b in Figure 9 that the low pressure area in this area of the embodiment of the present invention is smaller than that of the comparative prototype, that is, the leakage vortex at the blade tip is effectively controlled; at the same time, the blade tip of the embodiment of the present invention is The angle between the development trajectory of the leakage vortex and the blade increases, which also makes the leakage vortex move away from the blade suction surface. Figure 10 a and Figure 10 b are comparisons of turbulent kinetic energy distribution nephograms at 50% blade height section. According to the embodiment of the present invention, the turbulent kinetic energy intensity at the blade tip position is significantly reduced, that is, the vortex intensity in this area is reduced, which is consistent with the static pressure distribution characteristics. The reduction in leakage vortex intensity near the blade tip can effectively improve the noise performance of the air duct system. a in Figure 11, b in Figure 11, a in Figure 12 and b in Figure 12 are respectively the mean distribution of sound pressure pulsation on the surface of the axial flow blade and the air guide ring surface. As can be seen from the figure, using In the embodiment of the present invention, the average value of the sound pressure pulsation on the surface of the axial flow blade and the surface of the air guide ring is reduced. This is because the internal vortex near this area is weakened, and the irregular local pressure pulsation generated by it is weakened, and the local sound source is weakened. The intensity then diminishes.

The comparison of the air volume and noise parameters of the comparison group under the working condition of 954 rpm is shown in Table 2, and the comparison of the sound pressure level spectrum is shown in Figure 13.

Table 2 Comparison results of air volume and noise between the prototype and the embodiment of the present invention

Speed/rpm Air volume m ³ /h Power/W NoisedB Comparison prototype 954 2038 33.5 58.9 Example 954 2033 33.1 56.0 relative difference / -0.3% -1.2% -4.9%

Under the same rotation speed condition, the air volume of the embodiment and the comparison prototype is basically the same, the power is reduced by 1.2%, and the noise is reduced by 2.9dB. Compared with the current axial flow fan noise control scheme, the present invention uses a butterfly-type axial flow fan blade design to effectively improve the leakage vortex near the blade tip gap, weaken the pressure pulsation intensity on the blades and wind ring surfaces, and is basically ineffective in controlling the fan air volume. The aerodynamic performance of the fan is improved under changing conditions, and the fan power and fan eddy current noise are reduced.

Claims (4)

1. An axial flow blade structure, characterized in that it includes a blade body, the outer edge curve of the blade body is a characteristic curve S0, the characteristic curve S0 is a concave curve, and the two ends of the outer edge curve of the blade body are respectively axial flow wind blades. The blade outer edge leading edge point A and the axial flow blade outer edge trailing edge point B, the two ends of the characteristic curve S0 coincide with the axial flow blade outer edge leading edge point A and the axial flow blade outer edge trailing edge point B respectively. The leading edge point A of the outer edge of the axial flow blade is the intersection point of the blade leading edge line and the circle R=R2, the trailing edge point B is the intersection point of the blade trailing edge line and the circle R=R2, and the circle R=R2 is the axis with a uniform outer edge without depressions. The radius of the flow fan blade, the characteristic curve S0 is the outer edge profile of the imitation butterfly wing. The line connecting the leading edge point A of the axial flow fan blade and the trailing edge point B of the axial flow fan outer edge is the x direction, and the line perpendicular to the connecting line is In the y direction, the equation of the characteristic curve S0 is: Among them, k is a non-zero real number, R2/R3=0.96-0.98, R3 is the radius of the air guide ring, the difference between the maximum radius and the minimum radius of the outer edge of the axial flow blade is t, and the range of t/R3 is 0.01~0.05. 2. An axial flow fan based on the axial flow blade structure of claim 1, characterized in that it includes a blade hub (1100), a blade body (1200) and an air guide ring (1400). The blade body (1200) The circumferential array is fixed on the outer ring of the impeller hub (1100), and the air guide ring (1400) is sleeved on the outer ring of the blade body (1200). The axis of the impeller hub (1100) is connected with the rotation axis and air guide of the blade body (1200). The center lines of the circles (1400) coincide with each other, and the end of the air guide circle (1400) is connected to the fan shell. 3. The axial flow fan according to claim 2, characterized in that the air guide ring includes a circular arc section (1410), a vertical section (1420) and an outlet section (1430) connected in sequence, and the circular arc section (1410) ) is a tapered structure, and one end of the vertical section (1420) is connected to the minimum arc radius end of the arc section (1410). 4. A method for preparing an axial flow fan blade structure, which is characterized by comprising the following steps: S1, based on the outer edge profile data of the butterfly wing, equation fitting is used to establish the outer edge profile of the imitation butterfly wing; S2, take the direction of the line connecting the leading edge point and the trailing edge point of the outer edge of the butterfly wing as the x direction, and the vertical direction of the connection as the y direction, form the outer edge profile equation of the imitation butterfly wing, and scale the outer edge profile of the imitation butterfly wing as a whole Make its two end points coincide with the leading edge point of the outer edge of the axial flow blade and the trailing edge point of the outer edge of the axial flow blade respectively. The outer edge curve of the blade body is obtained as the characteristic curve. The characteristic curve is formed according to the outer edge curve of the blade body. Axial flow fan blade structure; The equation of the outer edge of the imitation butterfly wing is: Among them, k is a non-zero real number; the leading edge point A of the outer edge of the axial flow blade is the intersection point of the blade leading edge line and the circle R=R2, the trailing edge point B is the intersection point of the blade trailing edge line and the circle R=R2, and the circle R=R2 is the radius of the axial flow fan blade with a uniform outer edge and no depression, satisfying the relationship R2/R3=0.96-0.98, R3 is the radius of the air guide ring, the difference between the maximum radius and the minimum radius of the outer edge of the axial flow fan blade is t, and the range of t/R3 It is 0.01~0.05.