A frequency modulation method for changing welded iron blade structure of outer rotor axial flow fan

Abstract

The application discloses a frequency modulation method for changing the welded iron blade structure of an outer rotor axial flow fan, and the method steps are as follows: the blade is designed with a main reinforcing rib, the impeller after the design of the main reinforcing rib is calculated by using a finite element method, a Campbell diagram is drawn according to the commonly used rotating speed interval and the inherent frequency of the blade, whether there is a dangerous resonance in the commonly used rotating speed interval section is judged, if there is no dangerous resonance point, the blade is opened and tested and verified, and if there is a dangerous resonance point, the angle alpha and the thickness t of the main reinforcing rib of the blade need to be adjusted for frequency modulation, and the dangerous resonance point is judged again until there is no dangerous resonance point. The application is different from the prior art, the frequency of the blade is changed only by adjusting the angle of the reinforcing rib and increasing the thickness of the reinforcing rib without changing the shape of the blade material and redesigning the blade, the structure and method of frequency modulation of the blade are simplified, the frequency modulation of the blade is greatly facilitated, and the time and cost of frequency modulation of the blade are saved.

Description

Technical Field

[0001] This invention relates to the field of external rotor axial flow fan structure technology, and in particular to a frequency modulation method for changing the welded iron blade structure of an external rotor axial flow fan. Background Technology

[0002] External rotor axial flow fans are devices that provide wind energy and are widely used in various industries. Therefore, the reliability of these fans is receiving increasing attention. The impeller is a crucial component of the fan, and impeller failure is one of the main failure modes. Impeller failure can lead to the loss of the fan's basic functions, causing property damage and potentially even safety accidents.

[0003] Current analysis of the causes of wind turbine impeller failure generally considers them to be:

[0004] 1. Excessive impeller speed causes static stress to exceed the tensile strength of the material, leading to fracture;

[0005] 2. The impeller rotational speed frequency coincides with the impeller's natural frequency, resulting in resonance.

[0006] Therefore, it is necessary to change the blade frequency to avoid the resonant frequency and increase the tensile strength of the blade.

[0007] Existing common blade frequency tuning methods usually achieve this by changing the blade material or redesigning the blade by changing the blade thickness and shape. However, the selection of materials needs to consider many factors such as processing difficulty, manufacturing cost, and application environment. Changing the material simply for the purpose of frequency tuning is quite difficult. On the other hand, changing the blade thickness and shape to redesign the blade requires a lot of experimental processes and time, which is too costly and time-consuming. Summary of the Invention

[0008] To solve the above-mentioned technical problems, this invention designs a frequency modulation method for changing the structure of welded iron blades in an external rotor axial flow fan. While strengthening the tensile strength, the frequency of the blades can be changed by adjusting the angle and increasing the thickness of the reinforcing ribs. This can avoid the fracture accident caused by blade resonance and reduce the iteration of aerodynamic design.

[0009] The present invention adopts the following technical solution:

[0010] A frequency modulation method for modifying the welded iron blade structure of an external rotor axial flow fan, comprising the following steps:

[0011] S1. Perform finite element simulation analysis on the original blades that meet the fluid performance requirements to determine whether the static strength and deformation of the impeller meet the requirements, and select blades that meet the requirements.

[0012] S2. Design of the main reinforcing rib for the blade: A main reinforcing rib is formed by protruding outward at the center of the root of the curved blade. The arc surface formed by the protrusion of the main reinforcing rib is located at the root of the curved blade as the arc line L. L is parallel to the arc line at the root of the original blade. Let the starting point A1 of the main reinforcing rib and the starting point A2 of L form a straight line L1. Let the starting point A1 of the reinforcing rib and the starting point A2 of L form a straight line L2 at the point A3 corresponding to the curved surface of the original blade. L1 and L2 form an angle α. The thickness of the blade is t.

[0013] S3. Perform finite element analysis on the impeller after designing the main stiffeners. Draw a Campbell diagram based on the impeller's common speed range and the blade's natural frequency to determine if there is any dangerous resonance within the common speed range. If there is no dangerous resonance point, the blade is molded and tested for verification. If there is a dangerous resonance point, the included angle α and thickness t of the blade's main stiffeners need to be adjusted for frequency tuning. Increase α to increase the frequency, decrease α to decrease the frequency, increase t to increase the frequency, decrease t to decrease the frequency, and re-determine the dangerous resonance point until there is no dangerous resonance point.

[0014] Preferably, the size of the main reinforcing rib does not exceed 1 / 2 of the blade size.

[0015] Preferably, the blade and the main reinforcing rib are integrally stamped.

[0016] Preferably, auxiliary reinforcing ribs are formed by indentation on both sides of the main reinforcing rib at the root of the curved blade. The arc surface formed by the indentation of the auxiliary reinforcing ribs is located at the root of the curved blade, and the arc line is N, which is parallel to the arc line at the root of the original blade. Let the starting point B1 of the auxiliary stiffener and the starting point B2 of N form a straight line N1; let the starting point B1 of the stiffener and the starting point B2 of N form a straight line N2 at the point B3 corresponding to the original blade surface. N1 and N2 form an included angle β. Finite element analysis is performed on the impeller with main and auxiliary stiffeners. Based on the impeller's common speed range and the blade's natural frequency, a Campbell diagram is plotted to determine whether there is a dangerous resonance within the common speed range. If there is no dangerous resonance point, the blade is molded and tested for verification. If there is a dangerous resonance point, the included angle α and thickness t of the main stiffener and the included angle β of the auxiliary stiffener need to be adjusted for frequency tuning. Increase α, increase frequency; decrease α, decrease frequency; increase t, increase frequency; decrease t, decrease frequency; increase β, increase frequency; decrease β, decrease frequency, and re-determine the dangerous resonance point until there is no dangerous resonance point.

[0017] Preferably, the blade and the auxiliary reinforcing rib are integrally stamped.

[0018] Preferably, the upper limit of the included angle α is related to the plasticity of the material, and the lower limit of the included angle α is 0.

[0019] Preferably, the upper limit of the included angle β is related to the plasticity of the material, and the lower limit of the included angle β is 0.

[0020] Preferably, the lower limit of t is determined by the static strength of the blades meeting the maximum rotational speed of the impeller; the upper limit of t is limited by cost.

[0021] The beneficial effects of this invention are as follows: Unlike existing technologies, this invention designs a frequency modulation method by altering the structure of the welded iron blades in an external rotor axial flow fan. Without changing the blade material or redesigning the blades, the frequency is changed simply by adjusting the outward protrusion angle of the reinforcing ribs and increasing their thickness. This simplifies the structure and method of blade frequency modulation, greatly facilitating the process and saving time and cost. It also saves aerodynamic design iteration time, shortens the design cycle, and reduces verification costs. Within the commonly used speed range, it avoids resonance, enhances impeller reliability, and increases impeller lifespan. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the present invention;

[0023] Figure 2 This is a schematic diagram of the structure from another perspective of the present invention;

[0024] Figure 3 This is a diagram of the resonant rotational speed of the blade when the same included angle α and the thickness t is 1.2 mm.

[0025] Figure 4 This is a diagram of the resonant rotational speed of the blade when the same included angle α and the thickness t is 1.5 mm.

[0026] Figure 5 This is a diagram of the resonant rotational speed of the blade when the same included angle α and the thickness t is 2.0 mm.

[0027] Figure 6 It is based on Figures 3-5 Campbell plots were drawn using common speed ranges and blade natural frequency data.

[0028] Figure 7 This is a diagram of the resonant rotational speed of the blades of the present invention with the same thickness t and included angle α of 5 degrees.

[0029] Figure 8 This is a diagram of the resonant rotational speed of the blades of the present invention when the same thickness t and the included angle α are 10 degrees.

[0030] Figure 9 This is a diagram of the resonant rotational speed of the blades of the present invention when the same thickness t and the included angle α are 15 degrees.

[0031] Figure 10 It is based on Figures 7-9Campbell plots were drawn using common speed ranges and blade natural frequency data.

[0032] In the diagram: 1. Curved blade, 2. Main reinforcing rib, 3. Secondary reinforcing rib. Detailed Implementation

[0033] The technical solution of the present invention will be further described in detail below through specific embodiments and in conjunction with the accompanying drawings:

[0034] Example: Figure 1 and Figure 2 As shown, a frequency modulation method for changing the welded iron blade structure of an external rotor axial flow fan includes the following steps:

[0035] S1. Perform finite element simulation analysis on the original blades that meet the fluid performance requirements to determine whether the static strength and deformation of the impeller meet the requirements, and select blades that meet the requirements.

[0036] S2. Design of the main reinforcing rib for the blade: A main reinforcing rib is formed by protruding outward at the center of the root of the curved blade. The arc surface formed by the protrusion of the main reinforcing rib is located at the root of the curved blade as the arc line L. L is parallel to the arc line at the root of the original blade. Let the starting point A1 of the main reinforcing rib and the starting point A2 of L form a straight line L1. Let the starting point A1 of the reinforcing rib and the starting point A2 of L form a straight line L2 at the point A3 corresponding to the curved surface of the original blade. L1 and L2 form an angle α. The thickness of the blade is t.

[0037] S3. Perform finite element analysis on the impeller after designing the main stiffeners. Draw a Campbell diagram based on the impeller's common speed range and the blade's natural frequency to determine if there is any dangerous resonance within the common speed range. If there is no dangerous resonance point, the blade is molded and tested for verification. If there is a dangerous resonance point, the included angle α and thickness t of the blade's main stiffeners need to be adjusted for frequency tuning. Increase α to increase the frequency, decrease α to decrease the frequency, increase t to increase the frequency, decrease t to decrease the frequency, and re-determine the dangerous resonance point until there is no dangerous resonance point.

[0038] The size of the main reinforcing rib does not exceed 1 / 2 the size of the blade. The blade and the main reinforcing rib are formed by integral stamping.

[0039] Secondary reinforcing ribs are formed by indentation on both sides of the main reinforcing rib at the root of the curved blade. The arc surface formed by the indentation of the secondary reinforcing ribs is located at the root of the curved blade, and the arc line is N, which is parallel to the arc line at the root of the original blade. Let the starting point B1 of the auxiliary stiffener and the starting point B2 of N form a straight line N1; let the starting point B1 of the stiffener and the starting point B2 of N form a straight line N2 at the point B3 corresponding to the original blade surface. N1 and N2 form an included angle β. Finite element analysis is performed on the impeller with main and auxiliary stiffeners. Based on the impeller's common speed range and the blade's natural frequency, a Campbell diagram is plotted to determine whether there is a dangerous resonance within the common speed range. If there is no dangerous resonance point, the blade is molded and tested for verification. If there is a dangerous resonance point, the included angle α and thickness t of the main stiffener and the included angle β of the auxiliary stiffener need to be adjusted for frequency tuning. Increase α, increase frequency; decrease α, decrease frequency; increase t, increase frequency; decrease t, decrease frequency; increase β, increase frequency; decrease β, decrease frequency, and re-determine the dangerous resonance point until there is no dangerous resonance point.

[0040] The blades and auxiliary reinforcing ribs are integrally stamped. The upper limit of the included angle α is related to the plasticity of the material, and the lower limit of the included angle α is 0. The upper limit of the included angle β is also related to the plasticity of the material, and the lower limit of the included angle β is 0. The lower limit of t is determined by the static strength of the blades meeting the maximum speed of the impeller; the upper limit of t is limited by cost.

[0041] The table below shows the actual data results for the same included angle α but different thicknesses t:

[0042] Table 1 t=1.2mm

[0043] -- First order Second order Third order Static frequency 38.6 107.4 214.8 frequency 47.9 114.0 232.4

[0044] Table 2 t=1.5mm

[0045] -- First order Second order Third order Static frequency 43.9 123.4 251.8 frequency 52.1 129.0 266.8

[0046] Table 3 t=2.0mm

[0047] -- First order Second order Third order Static frequency 52.4 147.4 310.2 frequency 59.3 151.6 321.6

[0048] A blade resonance speed diagram is constructed from actual data results, such as... Figures 3-5 The figures shown are the blade resonance speed diagrams for the same included angle α and thicknesses t of 1.2 mm, 1.5 mm, and 2 mm, respectively. Figure 6 As shown in the Campbell diagram, mode1, mode2, and mode3 all move upwards as the thickness increases, indicating that the rotational frequency of the blades gradually increases with the increase in thickness.

[0049] The table below shows the actual data results for the same thickness t but different included angles α:

[0050] Table 4 α=5°

[0051] — Level 1 Level 2 Level 3 Static frequency 43.0 126.6 295.3 frequency 50.5 131.2 305.3

[0052] Table 5 α=10°

[0053] — Level 1 Level 2 Level 3 Static frequency 49.2 139.0 308.1 frequency 56.5 143.4 319.4

[0054] Table 6 α=15°

[0055] — Level 1 Level 2 Level 3 Static frequency 58.3 149.4 324.2 frequency 65.2 153.6 335.3

[0056] A blade resonance speed diagram is constructed from actual data results, such as... Figures 7-9 The figures shown are the blade resonance speed diagrams for thickness t and included angles α of 5 degrees, 10 degrees, and 15 degrees, respectively. Figure 10 As shown in the Campbell diagram, mode1, mode2, and mode3 all move upwards as the thickness increases, indicating that the rotational frequency of the blades gradually increases with the increase of the included angle α.

[0057] It can be seen that increasing α increases the frequency, decreasing α decreases the frequency, increasing β increases the frequency, decreasing β decreases the frequency, increasing t increases the frequency, decreasing t decreases the frequency, and by adjusting the blade frequency by adjusting the included angle α of the main stiffener, the included angle β of the auxiliary stiffener, and the blade thickness t, the resonant frequency can be avoided.

[0058] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Other variations and modifications are possible without departing from the technical solutions described in the claims.

Claims

1. A frequency modulation method for modifying the welded iron blade structure of an external rotor axial flow fan, characterized in that, The method and steps are as follows: S1. Perform finite element simulation analysis on the original blades that meet the fluid performance requirements to determine whether the static strength and deformation of the impeller meet the requirements, and select blades that meet the requirements. S2. Design of the main reinforcing rib for the blade: A main reinforcing rib is formed by protruding outward at the center of the root of the curved blade. The arc surface formed by the protrusion of the main reinforcing rib is located at the root of the curved blade as the arc line L. L is parallel to the arc line at the root of the original blade. Let the starting point A1 of the main reinforcing rib and the starting point A2 of L form a straight line L1. Let the starting point A1 of the main reinforcing rib and the starting point A2 of L form a straight line L2 at the point A3 corresponding to the curved surface of the original blade. L1 and L2 form an angle α. The thickness of the blade is t. S3. Perform finite element calculations on the impeller after designing the main stiffeners. Draw a Campbell diagram based on the impeller's common speed range and the blade's natural frequency to determine whether there is any dangerous resonance within the common speed range. If there is no dangerous resonance point, open the blade mold and conduct tests to verify it. If there is a dangerous resonance point, the included angle α and thickness t of the main stiffener of the blade need to be adjusted to tune the frequency. Increase α to increase the frequency, decrease α to decrease the frequency, increase t to increase the frequency, decrease t to decrease the frequency, and re-identify the dangerous resonance point until there is no dangerous resonance point.

2. The frequency modulation method for changing the welded iron blade structure of an external rotor axial flow fan according to claim 1, characterized in that, The size of the main reinforcing rib does not exceed 1 / 2 of the blade size.

3. The frequency modulation method for changing the welded iron blade structure of an external rotor axial flow fan according to claim 1, characterized in that, The blades and main reinforcing ribs are integrally stamped.

4. The frequency modulation method for changing the welded iron blade structure of an external rotor axial flow fan according to claim 1, characterized in that, Auxiliary reinforcing ribs are formed by indentation on both sides of the main reinforcing rib at the root of the curved blade. The arc surface formed by the indentation of the auxiliary reinforcing rib is located at the root of the curved blade as the arc line N. N is parallel to the arc line at the root of the original blade. Let the starting point B1 of the auxiliary reinforcing rib and the starting point B2 of N form a straight line N1. The starting point B1 of the auxiliary stiffener and the starting point B2 of N are connected to point B3 on the original blade surface to form a straight line N2. N1 and N2 form an included angle β. Finite element analysis is performed on the impeller with main and auxiliary stiffeners. Campbell's diagram is plotted based on the impeller's common speed range and the blade's natural frequency to determine whether there is a dangerous resonance within the common speed range. If there is no dangerous resonance point, the blade is molded and tested for verification. If there is a dangerous resonance point, the included angle α and thickness t of the main stiffener and the included angle β of the auxiliary stiffener need to be adjusted for frequency tuning. Increasing α increases the frequency, decreasing α decreases the frequency, increasing t increases the frequency, decreasing t decreases the frequency, increasing β increases the frequency, decreasing β decreases the frequency, and the dangerous resonance point is re-evaluated until there is no dangerous resonance point.

5. The frequency modulation method for changing the welded iron blade structure of an external rotor axial flow fan according to claim 4, characterized in that, The blades and auxiliary reinforcing ribs are integrally stamped.

6. The frequency modulation method for changing the welded iron blade structure of an external rotor axial flow fan according to claim 1, characterized in that, The upper limit of the included angle α is related to the plasticity of the material, and the lower limit of the included angle α is 0.

7. The frequency modulation method for changing the welded iron blade structure of an external rotor axial flow fan according to claim 4, characterized in that, The upper limit of the included angle β is related to the plasticity of the material, and the lower limit of the included angle β is 0.

8. The frequency modulation method for changing the welded iron blade structure of an external rotor axial flow fan according to claim 1, characterized in that, The lower limit of t is determined by the static strength of the blades needing to meet the maximum rotational speed of the impeller; the upper limit of t is limited by cost.

Images