Axial flow fan and wind speed monitoring system thereof

Abstract

This invention discloses an axial flow fan and its wind speed monitoring system, including a fan casing, a motor, an impeller, a bypass ventilation duct, and a measurement module. The motor is fixed inside the fan casing, and the impeller is fixed to the motor's drive shaft. The outer wall of the bypass ventilation duct is abutted and fixed to the outer wall of the fan casing. The measurement module includes a first sensor and a second sensor, which are diagonally arranged inside the bypass ventilation duct along its length. The line connecting the first and second sensors forms an angle with the length of the bypass ventilation duct. This invention, by setting a bypass ventilation duct on the outside of the fan casing, creates a wall-attached airflow on the side wall of the fan casing when the fan is working. The higher the wind speed inside the fan casing, the faster the wall-attached airflow. By monitoring the wall-attached airflow, the actual wind speed inside the fan casing can be calculated, which is not only highly accurate but also does not affect the airflow permeability within the fan casing.

Description

Technical Field

[0001] This invention relates to the field of fans, and more specifically, to an axial flow fan and its wind speed monitoring system. Background Technology

[0002] Axial flow fans are typically installed in highway and railway tunnels, primarily for ventilation, smoke exhaust, and environmental cooling within the tunnel. They are core equipment for ensuring the safe operation of tunnels. Therefore, real-time monitoring of the axial flow fan speed is crucial for determining the fan's operating status, ensuring ventilation effectiveness, and providing early warnings of potential malfunctions.

[0003] Currently, there are two main methods for monitoring the wind speed of traditional axial flow fans:

[0004] 1. Installing an anemometer directly inside the main air duct of the fan for real-time monitoring is possible, but the anemometer probe will intrude into the main airflow channel, obstructing the normal airflow, easily generating turbulence and eddies, disrupting the stability of the flow field inside the air duct, affecting the fan's ventilation efficiency, and increasing operating noise.

[0005] 2. Ultrasonic anemometers are installed at a distance in the tunnel space to indirectly measure and estimate the wind speed of the fans. However, this method is easily affected by factors such as tunnel length, curves, vehicle disturbances, and the coupled air supply of multiple fans. The measurement data has large dispersion and low accuracy, and cannot truly reflect the actual wind speed at the outlet of the axial flow fan. Therefore, there is an urgent need to improve this method. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide an axial flow fan and its wind speed monitoring system. By setting a bypass ventilation duct on the outside of the fan duct, when the fan is working, it will form a wall-attached airflow on the side wall of the fan duct. The greater the wind speed inside the fan duct, the faster the wall-attached airflow speed will be. By monitoring the wall-attached airflow, the actual wind speed inside the fan duct can be calculated. This method is not only highly accurate, but also does not affect the airflow passage inside the fan duct.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: an axial flow fan, comprising a fan casing, a motor, an impeller, a bypass ventilation duct, and a measurement module;

[0008] The motor is fixed inside the air duct, the impeller is fixed to the drive shaft of the motor, the outer wall of the bypass ventilation duct is abutted and fixed to the outer wall of the air duct, and the measurement module includes a first sensor and a second sensor. The first sensor and the second sensor are arranged diagonally inside the bypass ventilation duct along its length direction, and the line connecting the first sensor and the second sensor forms an angle with the length direction of the bypass ventilation duct.

[0009] Furthermore, the bypass ventilation duct includes an air inlet section, a variable diameter section, and a measuring section. The two ends of the variable diameter section are respectively connected to the air inlet section and the measuring section, and the cross-sectional dimension of the measuring section is smaller than that of the air inlet section.

[0010] Furthermore, both the first and second sensors are connected to the measuring section, the distance between the first and second sensors is greater than half the length of the duct, the inner wall of the first sensor is flush with the inner wall of the side ventilation duct, and the inner wall of the second sensor is flush with the inner wall of the side ventilation duct.

[0011] Furthermore, a rectifier grid is fixed inside the variable diameter section, and the air inlet section and the measuring section are connected through the rectifier grid;

[0012] The side ventilation duct is covered with a protective sleeve. One end of the protective sleeve is fixed to the end of the air inlet section. The outer contour of the protective sleeve is consistent with the outer contour of the air inlet section. An avoidance cavity is formed between the protective sleeve and the measuring section. The first sensor and the second sensor are fixed in the avoidance cavity.

[0013] Furthermore, the number of bypass ventilation ducts is at least two, and the multiple bypass ventilation ducts are evenly distributed along the axis of the ventilation duct;

[0014] Both the first and second sensors are ultrasonic anemometers.

[0015] It also includes a heat sink, a control box, an information processing module, and a prompting module. The information processing module and the prompting module are fixed inside the control box. The heat sink and the control box are both fixed to the outer wall of the air duct. The heat sink is located on the side of the control box facing both ends of the air duct and is parallel to the side ventilation duct.

[0016] A wind speed monitoring system includes an information processing module and an alerting module. The information processing module is electrically connected to both the measurement module and the alerting module. The information processing module performs the following steps:

[0017] S1. The wind speed along the oblique path between the first and second sensors is measured using the time difference method. ;

[0018] S2, to Angle compensation calculations were performed to obtain the axial wind speed inside the bypass ventilation duct. ;

[0019] S3, Calibrate Axial Wind Speed , obtain calibration value ;

[0020] S4. Based on the calibrated mapping coefficients , calibrate value Converted to wind speed inside the ventilation duct ;

[0021] S5. Complete real-time wind speed monitoring.

[0022] Furthermore, the mapping coefficients The process includes the following steps:

[0023] ① Obtained in the laboratory using a standard Pitot tube speed measuring device Group wind speed points, each group collects the actual wind speed along the axial direction of the wind tunnel. Actual axial wind speed of the bypass ventilation duct ,get Actual axial wind speed of the ventilation duct and Actual axial wind speed of the ventilation duct next to the group ;

[0024] ② Calculate the instantaneous mapping coefficients for each group. , ;

[0025] ③ To Group instantaneous mapping coefficients Take the average value to obtain the calibrated mapping coefficients. ;

[0026] .

[0027] Furthermore, in step S3, it is necessary to use sensor correction coefficients. Calibrate axial wind speed Sensor correction coefficient Obtaining it involves the following steps:

[0028] ① Obtaining standard speed measuring devices for pitot tubes At the same time, wind speeds were measured by the first and second sensors. Wind speed along the oblique path ;

[0029] ② Wind speed for each group Calculated and measured according to the included angle compensation Axial wind speed in the ventilation duct next to the group ;

[0030] The formula for calculating the included angle compensation is: ;

[0031] ③ Measure the axial wind speed in each group of bypass ventilation ducts. and the actual axial wind speed of each group of bypass ventilation ducts By comparing them one by one, we can obtain... Group instantaneous correction coefficient , ;

[0032] ④, Regarding Group instantaneous correction coefficient Take the average value to obtain the sensor correction coefficient. ;

[0033] .

[0034] Furthermore, calibration values The calculation formula is: ;

[0035] Airflow speed of the air duct The calculation formula is: .

[0036] Furthermore, there are two bypass ventilation ducts, which are evenly distributed along the axis of the ventilation duct, and there are two measurement modules, which correspond one-to-one with the bypass ventilation ducts.

[0037] The information processing module sets the allowable deviation threshold for the wind speed in the two bypass ducts. ;

[0038] Two sensor correction coefficients can be obtained through two measurement modules. Corrected calibration value and Calculate the difference ;

[0039] Difference With threshold Compare:

[0040] Difference ≤threshold The information processing module determines that both channels are normal, takes the average value as the effective wind speed, and calculates the average wind speed of the ventilation duct. ;

[0041] Average wind speed in the ventilation duct ;

[0042] Difference Greater than the threshold The system detects an malfunction in the measurement module, stops the motor, and issues an alarm.

[0043] In summary, the present invention has the following beneficial effects:

[0044] 1. This system adopts the standard laboratory testing method, using the axial wind speed of the bypass ventilation duct measured by the Pitot tube as the standard true value. The calculated axial wind speed obtained by the first and second sensors after angle compensation is corrected to reduce interference factors, improve stability, and achieve high-precision monitoring of wind speed. During on-site monitoring, the axial wind speed of the bypass ventilation duct after angle compensation and calibration is converted by the mapping coefficient obtained by laboratory testing, and finally accurately outputs the real-time wind speed in the ventilation duct.

[0045] 2. Both the first and second sensors are fixedly installed at the measurement section. By installing the first and second sensors at the measurement section, the flow velocity of the stabilized airflow adhering to the wall can be measured, resulting in higher measurement accuracy and lower error. Furthermore, the distance between the first and second sensors is greater than half the length of the duct, effectively ensuring a sufficiently long ultrasonic propagation path and significantly reducing measurement error. Due to the elongated structure of the measurement section, the included angle between the first and second sensors after installation is... It is small enough to reduce measurement errors while ensuring that the inner wall of the first sensor and the inner wall of the second sensor are flush with the inner wall of the side ventilation duct, thus preventing the measurement module from disrupting the stability of the airflow in the measurement section and improving measurement accuracy. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of the structure of this embodiment;

[0047] Figure 2 This is a cross-sectional view of this embodiment;

[0048] Figure 3 This is a partial sectional view of this embodiment;

[0049] Figure 4 for Figure 3 Enlarged view at point A;

[0050] Figure 5 This is a control principle diagram for this embodiment;

[0051] Figure 6 This is a diagram illustrating the execution steps of the information processing module in this embodiment.

[0052] Reference numerals: 1. Air duct; 11. Support frame; 12. Control box; 2. Motor; 3. Impeller; 4. Bypass ventilation duct; 41. Air inlet section; 42. Variable diameter section; 43. Measuring section; 5. First sensor; 6. Second sensor; 7. Rectifier grid; 8. Sheath; 81. First cover plate; 82. Second cover plate; 83. Clearance cavity; 9. Heat sink; 100. Measuring module; 200. Information processing module; 300. Indication module; 400. Indication light. Detailed Implementation

[0053] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0054] like Figures 1 to 6 As shown, this embodiment discloses an axial flow fan, including a fan duct 1, a motor 2, an impeller 3, a bypass ventilation duct 4, and a measurement module 100. The fan duct 1 is a cylindrical structure, and the motor 2 is a permanent magnet synchronous motor, which is fixed inside the fan duct 1 near the middle by a support frame 11 welded to the inner wall of the fan duct 1. The impeller 3 is fixedly connected to the drive shaft of the motor 2 and is directly driven to rotate by the motor 2 to realize continuous air supply from the motor 2 to the impeller 3.

[0055] like Figure 1 and Figure 2 As shown, the outer wall of the bypass ventilation duct 4 is tightly abutted against the outer wall of the air duct 1 and fixed to the air duct 1 with screws to ensure that there is no gap between the bypass ventilation duct 4 and the air duct 1. Since the bypass ventilation duct 4 is located outside the air duct 1, it will not cause any obstruction or disturbance to the airflow inside the air duct 1. Furthermore, the bypass ventilation duct 4 and the air duct 1 are parallel to each other, and the inlet and outlet of the bypass ventilation duct 4 correspond one-to-one with the inlet and outlet of the air duct 1. When airflow passes through the air duct 1, a portion of the wall-adhering airflow that flows through the outer wall of the air duct 1 will flow through the bypass ventilation duct 4, thereby forming a bypass airflow in the bypass ventilation duct 4.

[0056] like Figures 2 to 4 As shown, the bypass ventilation duct 4 includes an air inlet section 41, a variable diameter section 42, and a measuring section 43 arranged in sequence. The two ends of the variable diameter section 42 are welded and fixed to the air inlet section 41 and the measuring section 43, respectively. The cross-sectional dimension of the measuring section 43 is smaller than that of the air inlet section 41. After the airflow adhering to the wall of the ventilation duct 1 enters from the air inlet section 41, it is contracted and gathered by the variable diameter section 42 before entering the measuring section 43, making the airflow in the measuring section 43 more stable, which is beneficial to improving the accuracy of wind speed measurement in the bypass ventilation duct 4.

[0057] like Figure 4 As shown, a rectifier grid 7 is fixed inside the variable diameter section 42. The air inlet section 41 and the measuring section 43 are interconnected through the rectifier grid 7. The rectifier grid 7 is composed of grid-type plates, and each rectifier unit is square in shape. The rectifier grid 7 is existing technology. After setting the rectifier grid 7 inside the variable diameter section 42, it can not only solve the airflow disorder caused by the change in diameter, but also effectively straighten the airflow entering the measuring section 43, thereby improving the stability of the airflow and enabling the airflow to flow smoothly along the length direction of the measuring section 43.

[0058] like Figure 3 and Figure 4 As shown, the side ventilation duct 4 is covered with a protective sleeve 8. One end of the protective sleeve 8 is welded and fixed to the end of the air inlet section 41. The outer contour of the protective sleeve 8 is consistent with the outer contour of the air inlet section 41. Since the side ventilation duct 4 has a three-section structure, a stepped structure will be formed on the outer wall of the side ventilation duct 4, which will cause the airflow on the outer wall of the side ventilation duct 4 to be unstable. The unstable airflow will have a slight impact on the airflow inside the side ventilation duct 4. Therefore, by setting the protective sleeve 8, the stepped structure on the outer wall of the side ventilation duct 4 can be blocked. After the side ventilation duct 4 and the protective sleeve 8 are combined, the whole is smooth and the airflow stability is better.

[0059] like Figure 3 As shown, the measurement module 100 includes a first sensor 5 and a second sensor 6. Both sensors are existing ultrasonic anemometers, and are arranged diagonally inside the bypass ventilation duct 4 along its length. The line connecting the first sensor 5 and the second sensor 6 forms a fixed angle with the axial airflow direction of the bypass ventilation duct 4. This allows ultrasonic waves to propagate along an oblique air path inside the side ventilation duct 4, and wind speed is measured using the time difference method.

[0060] The time difference method measurement principle is as follows: both the first sensor 5 and the second sensor 6 have transmit and receive functions. By transmitting and receiving data from the two sensors, the downwind propagation time is measured. and headwind propagation time Let L be the distance along the oblique path between the first sensor 5 and the second sensor 6, and C be the velocity of sound in still air. Let the wind speed be along the diagonal path, then:

[0061] .

[0062] Both the first sensor 5 and the second sensor 6 are fixedly installed at the measurement section 43. By installing the first sensor 5 and the second sensor 6 at the measurement section 43, the flow velocity of the wall-mounted airflow after stabilization can be measured, resulting in higher measurement efficiency and lower error. Furthermore, the distance between the first sensor 5 and the second sensor 6 is greater than half the length of the duct 1. Specifically, the length of the duct 1 is 2.8m, and the oblique distance between the first sensor 5 and the second sensor 6 is 1.7m, which effectively ensures that the ultrasonic wave propagation path is long enough, greatly reducing measurement error.

[0063] like Figure 3 As shown, because the measuring section 43 is a long and narrow structure, the included angle between the first sensor 5 and the second sensor 6 after installation is... Small enough, the included angle in this embodiment This allows for the reduction of measurement errors while ensuring that the inner wall of the first sensor 5 is flush with the inner wall of the bypass ventilation duct 4, and the inner wall of the second sensor 6 is flush with the inner wall of the bypass ventilation duct 4, thus preventing the measurement module 100 from disrupting the stability of the airflow within the measurement section 43 and improving measurement accuracy.

[0064] like Figure 1 and Figure 4 As shown, a clearance cavity 83 is formed between the sheath 8 and the measuring section 43. The first sensor 5 and the second sensor 6 are fixed inside the clearance cavity 83. The sheath 8 can protect the measuring module 100. The sheath 8 is also equipped with a first cover plate 81 and a second cover plate 82 on its side wall. The first cover plate 81 and the second cover plate 82 are fixed to the sheath 8 by screws. The first cover plate 81 and the second cover plate 82 correspond one-to-one with the first sensor 5 and the second sensor 6, respectively. When maintenance is required, the corresponding sensor (first sensor 5 and second sensor 6) can be disassembled and installed simply by opening the corresponding cover plate (first cover plate 81 and second cover plate 82), which is convenient for maintenance.

[0065] like Figure 1 As shown, the number of bypass ventilation ducts 4 is at least two, and in this embodiment, two are preferred. The multiple bypass ventilation ducts 4 are evenly distributed along the axis of the air duct 1 to form a symmetrical dual-channel measurement structure, which is beneficial to improving the measurement accuracy and reliability of the system.

[0066] This embodiment also includes a heat sink 9, a control box 12, an information processing module 200, and a prompting module 300. The information processing module 200 and the prompting module 300 are both integrated and fixed inside the control box 12. The information processing module 200 is electrically connected to the measurement module 100 and the prompting module 300, respectively. The heat sink 9 and the control box 12 are both fixed to the outer wall of the air duct 1 with screws. The heat sink 9 is located on the side of the control box 12 facing both ends of the air duct 1. The heat sink 9 is parallel to the bypass ventilation duct 4. When the fan is running, a portion of the airflow close to the wall will flow through the heat sink 9 and contact the control box 12, thereby improving the heat dissipation effect on the control box 12.

[0067] This embodiment also discloses a wind speed monitoring system applied to the aforementioned axial flow fan. This system requires determining the mapping coefficient. and sensor correction coefficient Specifically, a standard air duct testing platform needs to be built in the laboratory, and the aforementioned axial flow fan needs to be tested in the laboratory to obtain the mapping coefficient. and sensor correction coefficient .

[0068] Mapping coefficients The process includes the following steps:

[0069] ① In a standard laboratory duct, the speed is obtained using a Pitot tube standard speed measuring device as specified in the national standard. Group wind speed points, each group simultaneously collects the actual wind speed along one axis of the ventilation duct. Actual axial wind speed of bypass ventilation duct 4 ;

[0070] get Actual axial wind speed of ventilation duct 1 ( )and Actual axial wind speed of ventilation duct 4 next to the group ( ), and then match the obtained data one by one;

[0071] ② Calculate the instantaneous mapping coefficient for each pair of data. Its calculation formula is ;

[0072] get Group mapping coefficients ( );

[0073] ③ To Group instantaneous mapping coefficients The average value is taken to obtain the final system calibration mapping coefficients. ;

[0074] .

[0075] Sensor correction coefficient Also obtained through laboratory truth value calibration:

[0076] ① Obtaining speed using a standard Pitot tube speed measuring device At the same time as the wind speed is measured, the first sensor 5 and the second sensor 6 simultaneously measure the wind speed. Wind speed along the oblique path ;

[0077] ②, the diagonal wind speed of each group Calculated based on the included angle compensation, and measured Axial wind speed inside group side ventilation duct 4 ;

[0078] The formula for calculating the included angle compensation is: ;

[0079] ③ Calculate the axial wind speed within each group of bypass ventilation ducts 4. and the actual axial wind speed of each group of bypass ventilation ducts 4 By comparing them one by one, the calculations were obtained. Group instantaneous correction coefficient , ;

[0080] ④, Regarding Group instantaneous correction coefficient Take the average value to obtain the sensor correction coefficient. ;

[0081] .

[0082] Obtaining mapping coefficients in the laboratory and sensor correction coefficient Then, the value is entered into the information processing module 200, and the information processing module 200 performs the following steps:

[0083] S1. The wind speed along the oblique path between the first sensor 5 and the second sensor 6 is measured using the time difference method. ;

[0084] S2, to Angle compensation calculations were performed to eliminate the influence of the angle, and the axial wind speed inside the bypass ventilation duct 4 was obtained. ;

[0085] S3, Correction coefficient via sensor Calibrate axial wind speed This reduces the impact of sensor installation, angle, and component errors, resulting in calibrated values. ;

[0086] Calibration value The calculation formula is: ;

[0087] S4. Based on the calibrated mapping coefficients , calibrate value Converted to wind speed inside ventilation duct 1 ;

[0088] Wind speed of air duct 1 The calculation formula is: ;

[0089] S5. Complete real-time wind speed monitoring.

[0090] This system employs standard laboratory testing methods, using pitot tubes to measure the 4-axis wind speed in the bypass duct. The calculated axial wind speed is obtained by compensating the included angle between the first sensor 5 and the second sensor 6, using the standard true value. Error correction is performed to reduce interference factors, resulting in good stability and high-precision wind speed monitoring. During on-site monitoring, the axial wind speed of bypass duct 4 is measured after angle compensation and calibration. The mapping coefficients were then obtained through laboratory testing. The final accurate output shows the real-time wind speed inside duct 1. .

[0091] Since there are two bypass ducts 4 and two measurement modules 100 corresponding one-to-one with each bypass duct 4, under completely normal conditions, the data from the two measurement modules 100 will not be completely equal due to factors such as sensor accuracy, minor airflow disturbances, and device variability. Natural deviations are inevitable. To prevent the system from misinterpreting normal fluctuations as faults, and to avoid frequent false alarms due to a fault in one module, thus affecting monitoring stability, the system needs to set a maximum permissible deviation threshold for the calculated axial wind speed values ​​of the two modules. It is used to determine whether the sensor is malfunctioning or being interfered with;

[0092] Allowable deviation threshold for wind speed in two bypass ventilation ducts The method of obtaining it includes the following steps:

[0093] S1. In the standard laboratory duct, the velocity of two bypass ducts 4 is simultaneously measured using a Pitot tube standard velocity measuring device as specified in the national standard. Group wind speed points, each group collects the actual axial wind speed of the bypass ventilation duct 4. Two data collection streams were used to obtain the following results: and ;

[0094] S2. Compare the data obtained simultaneously from both sources one by one. The comparison method is as follows: Finally, a set of natural difference sequences under normal conditions is obtained. ;

[0095] S3. Take the average of the sequence differences. To allow for a safety margin and avoid misinterpreting normal fluctuations as abnormal, a deviation threshold is set. ,Pick .

[0096] Information processing module 200 sets the allowable deviation threshold for the wind speed of the two bypass ventilation ducts. Two sensor correction coefficients can be obtained through two measurement modules 100. Corrected calibration value and Calculate the difference ;

[0097] Difference With threshold Compare:

[0098] Difference ≤threshold The information processing module 200 determines that both channels are normal, takes the average value as the effective wind speed, and calculates the average wind speed of duct 1. ;

[0099] Average wind speed in the ventilation duct ;

[0100] Difference Greater than the threshold If the measurement module 100 is found to be abnormal, the motor 2 will stop working, and the prompt module 300 will issue an alarm, and the indicator light 400 will remain on, reminding staff to investigate the cause of the abnormality. If the abnormal channel returns to normal, the system will automatically resume the dual-channel average calculation. However, in the event of a fire, the fan will continue to work continuously regardless of whether the measurement module 100 is abnormal, to ensure ventilation and smoke exhaust safety.

[0101] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. An axial flow fan, characterized in that, It includes a ventilation duct (1), a motor (2), an impeller (3), a bypass ventilation duct (4), and a measurement module (100); The motor (2) is fixed inside the air duct (1), the impeller (3) is fixed to the drive shaft of the motor (2), the outer wall of the bypass ventilation duct (4) is fixed to the outer wall of the air duct (1), and the measuring module (100) includes a first sensor (5) and a second sensor (6). The first sensor (5) and the second sensor (6) are arranged diagonally inside the bypass ventilation duct (4) along its length direction, and the line connecting the first sensor (5) and the second sensor (6) forms an angle with the length direction of the bypass ventilation duct (4).

2. An axial flow fan according to claim 1, characterized in that, The bypass ventilation duct (4) includes an air inlet section (41), a variable diameter section (42), and a measuring section (43). The two ends of the variable diameter section (42) are connected to the air inlet section (41) and the measuring section (43), respectively. The cross-sectional dimension of the measuring section (43) is smaller than that of the air inlet section (41).

3. An axial flow fan according to claim 2, characterized in that, The first sensor (5) and the second sensor (6) are both connected to the measuring section (43). The distance between the first sensor (5) and the second sensor (6) is greater than half the length of the duct (1). The inner wall of the first sensor (5) is flush with the inner wall of the bypass ventilation duct (4), and the inner wall of the second sensor (6) is flush with the inner wall of the bypass ventilation duct (4).

4. An axial flow fan according to claim 2, characterized in that, A rectifier grid (7) is fixed inside the variable diameter section (42), and the air inlet section (41) and the measuring section (43) are connected through the rectifier grid (7); The side ventilation duct (4) is covered with a protective sleeve (8). One end of the protective sleeve (8) is fixed to the end of the air inlet section (41). The outer contour of the protective sleeve (8) is consistent with the outer contour of the air inlet section (41). A clearance cavity (83) is formed between the protective sleeve (8) and the measuring section (43). The first sensor (5) and the second sensor (6) are fixed in the clearance cavity (83).

5. An axial flow fan according to claim 1, characterized in that, The number of the bypass ventilation ducts (4) is at least two, and the multiple bypass ventilation ducts (4) are evenly distributed along the axis of the air duct (1); Both the first sensor (5) and the second sensor (6) are ultrasonic wind speed sensors; It also includes a heat sink (9), a control box (12), an information processing module (200), and a prompting module (300). The information processing module (200) and the prompting module (300) are fixed inside the control box (12). The heat sink (9) and the control box (12) are both fixed to the outer wall of the air duct (1). The heat sink (9) is located on the side of the control box (12) facing both ends of the air duct (1). The heat sink (9) is parallel to the bypass ventilation duct (4).

6. A wind speed monitoring system, applied to an axial flow fan as described in any one of claims 1-5, characterized in that, It includes an information processing module (200) and a prompting module (300), wherein the information processing module (200) is electrically connected to the measurement module (100) and the prompting module (300) respectively, and the information processing module (200) performs the following steps: S1. The wind speed along the oblique path between the first sensor (5) and the second sensor (6) is measured using the time difference method. ; S2, to Angle compensation calculations were performed to obtain the axial wind speed inside the bypass ventilation duct (4). ; S3, Calibrate Axial Wind Speed , obtain calibration value ; S4. Based on the calibrated mapping coefficients , calibrate value Converted to wind speed inside the ventilation duct (1) ; S5. Complete real-time wind speed monitoring.

7. A wind speed monitoring system according to claim 6, characterized in that, The mapping coefficients The process includes the following steps: ① Obtained in the laboratory using a standard Pitot tube speed measuring device Group wind speed points, each group collects the actual axial wind speed of the wind tunnel (1). The actual axial wind speed of the bypass ventilation duct (4) ,get Actual axial wind speed of the ventilation duct (1) and Actual axial wind speed of the ventilation duct (4) next to the group ; ② Calculate the instantaneous mapping coefficients for each group. , ; ③ To Group instantaneous mapping coefficients Take the average value to obtain the calibrated mapping coefficients. ; 。 8. A wind speed monitoring system according to claim 7, characterized in that, In step S3, it is necessary to use sensor correction coefficients. Calibrate axial wind speed Sensor correction coefficient Obtaining it involves the following steps: ① Obtaining standard speed measuring devices for pitot tubes At the same time, the wind speed is measured by the first sensor (5) and the second sensor (6). Wind speed along the oblique path ; ② Wind speed for each group Calculated and measured according to the included angle compensation Axial velocity inside the ventilation duct (4) next to the group ; The formula for calculating the included angle compensation is: ; ③ The axial wind speed in each group of bypass ventilation ducts (4) and the actual axial wind speed of each group of bypass ventilation ducts (4) By comparing them one by one, we can obtain... Group instantaneous correction coefficient , ; ④, Regarding Group instantaneous correction coefficient Take the average value to obtain the sensor correction coefficient. ; 。 9. A wind speed monitoring system according to claim 8, characterized in that, Calibration value The calculation formula is: ; Wind speed of ventilation duct (1) The calculation formula is: .

10. A wind speed monitoring system according to claim 8, characterized in that, There are two bypass ventilation ducts (4) and they are evenly distributed along the axis of the ventilation duct (1). There are two measurement modules (100) and they correspond one-to-one with the bypass ventilation ducts (4). The information processing module (200) sets the allowable deviation threshold for the wind speed of the two bypass ventilation ducts (4). ; Two sensor correction coefficients can be obtained through two measurement modules (100). Corrected calibration value and Calculate the difference ; Difference With threshold Compare: Difference ≤threshold The information processing module (200) determines that both channels are normal, takes the average value as the effective wind speed, and calculates the average wind speed of the duct (1). ; Average wind speed in duct (1) ; Difference Greater than the threshold If the measurement module (100) is found to be abnormal, the motor (2) will stop working and an alarm will be issued at the same time.

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