Bypass fan based on a biomimetic structure

Abstract

The application discloses a ducted fan based on a bionic structure, which comprises a driving motor, a propeller and a duct body; the driving motor is used for driving the propeller to rotate; the propeller is arranged in a space surrounded by the duct body; a bird feather-shaped groove is arranged on an inner wall surface of the duct body, a plurality of groups of the bird feather-shaped grooves are arranged in a circumferential direction of the surface wall of the duct body, the plurality of groups of the bird feather-shaped grooves are arranged in an axial direction of the duct body, and groove angles of adjacent bird feather-shaped grooves are opposite in sign; the bird feather-shaped groove is introduced on the surface of the duct body, the gas flow of the wall surface of the duct body is improved, and the overall operation noise is reduced; moreover, the ducted fan has a good application prospect in noise reduction compared with a reference fan, the original duct profile design appearance and the cooperation relationship between the propeller and the duct are not changed, and the ducted fan has more transformability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ducted fans, and particularly relates to a ducted fan based on a bionic structure. BACKGROUND

[0002] With the deepening of the concept of low-altitude economy, the development of electric vertical take-off and landing (eVTOL) aircraft is also in full swing. As a high-efficiency propulsion unit, the application of ducted fans in eVTOL has great prospects, and a large number of related companies and institutions are constantly improving the design of ducted fans.

[0003] A ducted fan mainly consists of a propeller, a duct shell and a driving motor, and mainly shows a fan structure in which a hard shell wraps the propeller. The shell not only protects ground personnel from being injured by the propeller, but also isolates the propeller from the interference of the external harsh environment to some extent. Moreover, the shell can suppress the propeller tip vortex and straighten the front airflow, thereby improving the overall operating efficiency.

[0004] Studies have shown that, under the same input power, the thrust generated by a ducted fan is nearly twice that of an isolated propeller. In terms of noise, the ducted fan also has excellent noise reduction performance. The duct wall can act as a noise reflection surface to isolate the tonal noise and broadband noise caused by the propeller tip vortex shedding, thereby achieving a noise shielding effect, which is of great significance for future eVTOL operation in urban low-altitude operation.

[0005] The main difficulty in the design optimization of a ducted fan is to balance the thrust performance and noise performance. Previous researchers mainly focused on the wing profile shape of the duct, the shape of the propeller and the matching method of the duct and the propeller. Since the 1950s, a large number of studies have been based on the above design objectives.

[0006] However, there is a lack of in-depth research on how to further reduce the noise of the ducted fan. Therefore, how to further reduce the noise of the ducted fan has become a problem to be solved by those skilled in the art. SUMMARY

[0007] The present application relates to the technical field of ducted fans, and particularly relates to a ducted fan based on a bionic structure.

[0008] In order to solve the above technical problems, the application provides a ducted fan based on a bionic structure, which comprises a driving motor, a propeller and a duct body; the driving motor is used for driving the propeller to rotate; the propeller is arranged in a space surrounded by the duct body; a bird feather-shaped groove is arranged on an inner wall surface of the duct body; a plurality of groups of the bird feather-shaped grooves are arranged in a circumferential direction around the surface wall of the duct body; the plurality of groups of the bird feather-shaped grooves are all arranged in an axial direction of the duct body, and groove angles of adjacent bird feather-shaped grooves are opposite in sign.

[0009] In one of the embodiments, a wing tip gap is left between a wing tip of the propeller and the inner wall surface of the duct body, and the wing tip gap is within 0.5% to 1% of a diameter of the propeller.

[0010] In one of the embodiments, a cross section of the duct body is an NACA0018 airfoil.

[0011] In one of the embodiments, a support frame is arranged in the space surrounded by the duct body, the support frame is integrally formed with the duct body, and the driving motor and the propeller are mounted on the support frame.

[0012] In one of the embodiments, the support frame comprises a support seat and a baffle; the support seat is arranged at a center of the space surrounded by the duct body, the driving motor and the propeller are mounted on the support seat; and a plurality of the baffles are connected between the inner wall of the duct body and an outer wall of the support seat.

[0013] In one of the embodiments, the baffle is an NACA0012 airfoil.

[0014] In one of the embodiments, in the circumferential direction, the groove angles of adjacent bird feather-shaped grooves are opposite in sign at intervals of 10° to 20°.

[0015] In one of the embodiments, an attack angle of the bird feather-shaped groove is 15° to 20°.

[0016] The application has the following beneficial effects:

[0017] The application introduces the bird feather-shaped groove on the surface of the duct body, improves the gas flow of the wall surface of the duct body, and reduces the overall operation noise; moreover, the ducted fan has a good application prospect in noise reduction compared with the benchmark fan, does not change the original duct cross section design shape and the matching relationship between the propeller and the duct, and has more transformability. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the present application, the drawings required to be used in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description only constitute some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0019] Figure 1 is a structural schematic diagram provided by an embodiment of the present application;

[0020] Figure 2 is a structural schematic diagram provided by an embodiment of the present application; Figure 1 is a partial sectional structural schematic diagram of the channel body;

[0021] Figure 3 is a structural schematic diagram provided by an embodiment of the present application; Figure 1 is a schematic diagram of a bird feather-shaped groove layout mode;

[0022] Figure 4 is a structural schematic diagram provided by an embodiment of the present application; Figure 3 is an enlarged structural schematic diagram of part A of the channel fan;

[0023] Figure 5 is a structural schematic diagram provided by an embodiment of the present application; Figure 1 is a structural schematic diagram of a support frame;

[0024] Figure 6 is a structural schematic diagram of a reference channel fan of a comparison test;

[0025] Figure 7 is a structural schematic diagram of a bird feather-shaped groove external structure of a comparison test channel fan;

[0026] Figure 8 is an OASPL azimuth angle distribution of a channel fan Figure 1 ;

[0027] Figure 9 is an OASPL azimuth angle distribution of a channel fan Figure 2 ;

[0028] Figure 10 is an OASPL azimuth angle distribution of a channel fan Figure 3 ;

[0029] Figure 11 is an OASPL azimuth angle distribution of a channel fan Figure 4 ;

[0030] Figure 12 is an OASPL azimuth angle distribution of a channel fan Figure 5 ;

[0031] Figure 13 is an OASPL azimuth angle distribution of a channel fan Figure 6 ;

[0032] Figure 14Bypass fan OASPL azimuthal distribution Figure 7 ;

[0033] Figure 15 Bypass fan OASPL azimuthal distribution Figure 8 ;

[0034] Figure 16 Bypass fan spectral characteristic curve at 20 m / s incoming flow speed Figure 1 ;

[0035] Figure 17 Bypass fan spectral characteristic curve at 20 m / s incoming flow speed Figure 2 ;

[0036] Figure 18 Bypass fan spectral characteristic curve at 20 m / s incoming flow speed Figure 3 ;

[0037] Figure 19 Bypass fan spectral characteristic curve at 20 m / s incoming flow speed Figure 4 .

[0038] Reference signs are as follows:

[0039] 10. Driving motor;

[0040] 20. Propeller;

[0041] 30. Bypass body;

[0042] 40. Bird feather-shaped groove;

[0043] 50. Supporting frame; 51. Supporting seat; 52. Straightener. DETAILED DESCRIPTION

[0044] The technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application.

[0045] The present application provides a bypass fan based on bionic structure, a first embodiment thereof is shown in Figures 1 to 5 , comprising a driving motor 10, a propeller 20 and a bypass body 30.

[0046] Regarding the driving motor 10, as shown in Figure 1 , this embodiment sets the driving motor 10 to drive the propeller 20 to rotate, so only the rotating shaft of the driving motor 10 needs to be connected and fixed with the propeller 20, and the driving motor 10 can generate driving force to control the propeller 20 to rotate at high speed.

[0047] Regarding the propeller 20, as shown in Figure 1As shown, the propeller 20 is arranged in the space enclosed by the duct 30 to isolate the interference of the harsh environment on the operation of the propeller 20; and at this time, the wing tip gap between the wing tip of the propeller 20 and the inner wall of the duct 30 is within 0.5% to 1% of the diameter of the propeller 20, for example, the wing tip gap of the propeller 20 in this embodiment is 1% of the diameter of the propeller 20.

[0048] The main reasons for the above design are as follows:

[0049] 1. Ensure sufficient propulsion efficiency. If the wing tip gap is too small, the airflow velocity gradient between the wing tip of the propeller 20 and the inner wall of the duct 30 will increase, resulting in increased frictional resistance and reduced propulsion efficiency. Moreover, manufacturing errors or material thermal expansion may cause the wing tip of the propeller 20 to contact the inner wall of the duct 30, causing mechanical damage or vibration.

[0050] If the wing tip gap is too large, the wing tip vortex will be enhanced. For example, when the propeller 20 rotates, the high pressure difference at the wing tip of the propeller 20 will form a strong wing tip vortex, resulting in energy loss. A large wing tip gap will weaken the suppression of the duct on the vortex, thereby reducing the propulsion efficiency. Moreover, the flow guiding effect of the duct cannot be fully exerted at this time, and the thrust of the propeller 20 may also decrease.

[0051] 2. Reduce aerodynamic noise. If the wing tip gap is too small, the airflow will accelerate in the narrow wing tip gap and form a turbulent boundary layer, producing high-frequency noise. If the wing tip gap is too large, the uncontrolled wing tip vortex will interact with the inner wall of the duct 30, resulting in an increase in low-frequency vortex noise. Therefore, appropriately reducing the wing tip gap will suppress the wing tip vortex, thereby reducing the overall noise level.

[0052] 3. Reduce vibration to improve stability. If the wing tip gap is too small, the potential contact between the wing tip of the propeller 20 and the duct 30 will cause structural vibration, and even resonance, threatening mechanical reliability. If the wing tip gap is too large, unstable wing tip vortexes may induce internal airflow pulsation of the duct 30, causing the propeller 20 or the duct to vibrate.

[0053] 4. Improve mechanical reliability. If the wing tip gap is too small, long-term micro-contact or airflow impact may accelerate the fatigue damage of the wing tip of the propeller 20 or the inner wall of the duct 30. Moreover, material expansion under high temperature conditions may further reduce the gap and increase the risk. If the wing tip gap is too large, it will cause uneven aerodynamic load. Uneven flow may cause the propeller 20 to fluctuate in stress, shortening the service life of the components.

[0054] 5、Reduce the processing and maintenance costs, because if the wing tip gap is too small, the need for higher manufacturing precision (such as precision machining or composite material forming), increasing production costs, and frequent inspection of the gap changes during maintenance to avoid performance degradation due to wear or deformation; if the wing tip gap is too large, although it can reduce the manufacturing and maintenance costs, but may sacrifice the aerodynamic efficiency or noise performance.

[0055] 6, Ensure that the hover efficiency can be met, because small gap can improve hover efficiency, but need to balance the influence of noise and vibration on the sensor.

[0056] In summary, the size of the wing tip gap will have a multi-faceted impact on the duct fan, and after a large number of experimental verification, it is found that the wing tip gap within 0.5% to 1% of the diameter of the propeller 20 will obtain the best comprehensive performance effect, for example, setting the wing tip gap to 1% of the diameter of the propeller 20 is a preferred scheme.

[0057] It should be pointed out that in order to realize the installation of the driving motor 10 and the propeller 20, the setting mode shown in Figure 1 and Figure 5 is adopted at this time, that is, the space surrounded by the duct body 30 is provided with a support frame 50, the support frame 50 is integrally formed with the duct body 30, and the driving motor 10 and the propeller 20 are installed on the support frame 50.

[0058] Specifically, the support frame 50 at this time includes a support seat 51 and a rectifier sheet 52; the support seat 51 is in the shape of a cylinder, the support seat 51 is arranged at the center of the space surrounded by the duct body 30, and the driving motor 10 and the propeller 20 are installed on the support seat 51; a plurality of rectifier sheets 52 are connected between the inner wall of the duct body 30 and the outer wall of the support seat 51, for example, the rectifier sheet 52 of this embodiment is four, and the four rectifier sheets 52 are arranged on the four sides of the support seat 51 in the form of equal intervals, so that the support frame 50 is roughly cross-shaped as a whole.

[0059] Since the driving motor 10 and the propeller 20 are connected and fixed, only the driving motor 10 needs to be connected and fixed with the support seat 51, so as to realize the installation and fixation of the driving motor 10 and the propeller 20 on the support frame 50.

[0060] Further, the rectifier sheet 52 of this embodiment is NACA0012 airfoil, which at least has the following beneficial effects by adopting this setting mode:

[0061] 1. The upper and lower surfaces of the NACA0012 airfoil are completely symmetrical, and the forward and reverse flow performances are consistent, so there is no need to distinguish the installation direction, thereby reducing the risk of performance loss due to incorrect direction.

[0062] 2. It has the characteristics of low resistance and high flow control efficiency, for example, its resistance is smallest at zero angle of attack, and its resistance coefficient Cd ≈0.006, suitable for scenarios requiring smooth flow guide; not only can reduce turbulence and pressure drop resistance in high-speed flow, but also can suppress airflow separation, such as NACA0012 airfoil boundary layer is more stable at higher Reynolds number (Re>1×10 6 ) to avoid premature separation.

[0063] 3. Performance advantage at high Reynolds number, better performance in transonic or high-speed flow, such as NACA0012 airfoil delays shock wave generation, reduces wave resistance, and NACA0012 airfoil responds faster to air flow disturbance.

[0064] 4. Lightweight structure and convenient manufacturing, NACA0012 airfoil thickness reduces weight while ensuring strength, more suitable for weight-sensitive applications (such as unmanned aerial vehicles, spacecraft); and NACA0012 airfoil symmetric design simplifies mold manufacturing (such as injection molding or 3D printing), suitable for standardized production, reducing costs.

[0065] 5. Wide angle of attack adaptability, such as NACA0012 airfoil has the highest efficiency at zero angle of attack, but NACA0012 airfoil can still maintain low resistance and low turbulence within ±8° angle of attack, and it has complex flow field adaptability, which can reduce performance fluctuations in non-uniform flow.

[0066] 6. Low noise characteristics, NACA0012 airfoil has almost no separation flow at zero angle of attack, thereby reducing turbulent pulsating noise.

[0067] Regarding the duct body 30, as shown in Figures 1 to 4 , the inner wall surface of the duct body 30 is provided with a bird feather-shaped groove 40, a plurality of bird feather-shaped grooves 40 are arranged circumferentially around the surface wall of the duct body 30, a plurality of bird feather-shaped grooves 40 are arranged along the axial direction of the duct body 30, and the groove angles of adjacent bird feather-shaped grooves 40 are opposite in sign, so that the bird feather-shaped grooves 40 present a periodic distribution structure of upward sharp split, downward sharp split, and upward sharp split, at this time the shape is roughly herringbone-shaped.

[0068] For the present application, the bird feather-shaped groove 40 is the core of the whole scheme and the key point of reducing noise, so as to better reflect the importance of the bird feather-shaped groove 40, the following will be explained in combination with specific comparative examples.

[0069] This comparative experiment is a noise test of the duct fan, mainly comparing the noise performance of the baseline duct fan with a NACA0018 airfoil cross section (as shown in Figure 6 ) and three different design parameter duct fans (provided with bird feather-shaped grooves 40) under the condition of having flow, 0°-15° angle of attack.

[0070] Test conditions: 10m / s-20m / s incoming flow velocity, interval 2m / s; 0°-15° attack angle, interval 5°. The propeller 20 rotating speed is fixed at 5000RPM. The microphone voltage data is obtained by testing, and the overall sound pressure level (OASPL) distribution with azimuth angle and the noise spectrum characteristics curve of the ducted fan are obtained after processing, wherein the test duct type is as follows:

[0071]

[0072] The specific test results are shown in Figures 8 to 15

[0073] Figure 7 is the OASPL distribution diagram of the ducted fan under 0° attack angle and 10m / s front incoming flow when the bird feather-shaped groove 40 is set in the duct body 30. Figure 8

[0074] Figure 8 is the OASPL distribution diagram of the ducted fan under 0° attack angle and 20m / s front incoming flow when the bird feather-shaped groove 40 is set in the duct body 30. Figure 9

[0075] Figure 9 is the OASPL distribution diagram of the ducted fan under 5° attack angle and 10m / s front incoming flow when the bird feather-shaped groove 40 is set in the duct body 30. Figure 10

[0076] Figure 10 is the OASPL distribution diagram of the ducted fan under 5° attack angle and 20m / s front incoming flow when the bird feather-shaped groove 40 is set in the duct body 30. Figure 11

[0077] Figure 11 is the OASPL distribution diagram of the ducted fan under 10° attack angle and 10m / s front incoming flow when the bird feather-shaped groove 40 is set in the duct body 30. Figure 12

[0078] Figure 12 is the OASPL distribution diagram of the ducted fan under 10° attack angle and 20m / s front incoming flow when the bird feather-shaped groove 40 is set in the duct body 30. Figure 13

[0079] Figure 13 is the OASPL distribution diagram of the ducted fan under 15° attack angle and 10m / s front incoming flow when the bird feather-shaped groove 40 is set in the duct body 30. Figure 14

[0080] Figure 14 is the OASPL distribution diagram of the ducted fan under 15° attack angle and 20m / s front incoming flow when the bird feather-shaped groove 40 is set in the duct body 30. Figure 15 The results show that under low flow speed and low attack angle, the noise reduction effect of the duct with the bird feather-shaped groove 40 is limited compared with the reference duct, and even in some cases it may increase certain noise. Under high flow speed and high attack angle conditions, whether the bird feather-shaped groove 40 is set inside the duct body 30 (i.e.

[0081] Figure 1 ​is inside (i.e. Figure 7 As shown in the table below, the maximum noise reduction effect appears at the azimuth angle of 65°, i.e. near the inlet of the duct.

[0082]

[0083] As shown in the table above, the maximum noise reduction effect appears at the azimuth angle of 65°, i.e. near the inlet of the duct.

[0084] Now the spectral characteristics at the azimuth angle of 45° are analyzed to explore the main frequency band of the groove structure for noise reduction. Figures 16 to 19 As shown in the table above, the maximum noise reduction effect appears at the azimuth angle of 65°, i.e. near the inlet of the duct.

[0085] Therefore, the setting parameters of the bird feather-shaped groove 40 are very important to the performance of the duct, so as to ensure that the duct fan with the bird feather-shaped groove 40 can meet the requirements of the design concept, it is suggested that in the circumferential direction, every 10°-20°, the groove angles of adjacent bird feather-shaped grooves 40 are opposite, and the attack angle of the bird feather-shaped groove 40 is 15°-20°; for example, as shown in the table above, this embodiment sets every 15°, the groove angles of adjacent bird feather-shaped grooves 40 are opposite, and the attack angle of the bird feather-shaped groove 40 is 15°. Figure 3 As shown in the table above, the maximum noise reduction effect appears at the azimuth angle of 65°, i.e. near the inlet of the duct. Figure 4 As shown in the table above, the maximum noise reduction effect appears at the azimuth angle of 65°, i.e. near the inlet of the duct.

[0086] It should be pointed out that, as shown in the table above, this embodiment sets the profile of the duct body 30 as a NACA0018 airfoil. Figure 2

[0087] The above is the preferred embodiment of the present application, it should be pointed out that for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, these improvements and refinements are also considered to be within the scope of protection of the present application.​

Claims

1. A ducted fan based on a biomimetic structure, characterized in that, Includes drive motor, propeller and duct; The drive motor is used to drive the propeller to rotate; The propeller is located within the space enclosed by the duct body; The inner wall of the culvert is provided with bird feather-shaped grooves. Multiple sets of bird feather-shaped grooves are arranged circumferentially around the wall of the culvert. All sets of bird feather-shaped grooves extend along the axial direction of the culvert, and the groove angles of adjacent bird feather-shaped grooves are opposite. In the circumferential direction, the groove angles of adjacent bird feather-shaped grooves are opposite every 10° to 20°. The angle of attack of the bird feather-shaped groove is 15°~20°.

2. The ducted fan according to claim 1, characterized in that, A wingtip gap is provided between the wingtip of the propeller and the inner wall of the duct, and the wingtip gap is within 0.5% to 1% of the diameter of the propeller.

3. The ducted fan according to claim 1, characterized in that, The cross-section of the duct body is NACA0018 airfoil.

4. The ducted fan according to claim 1, characterized in that, A support frame is provided within the space enclosed by the culvert body. The support frame is integrally formed with the culvert body, and the drive motor and the propeller are installed on the support frame.

5. The ducted fan according to claim 4, characterized in that, The support frame includes a support base and rectifier plates; The support base is located at the center of the space enclosed by the culvert body, and the drive motor and the propeller are installed on the support base. Multiple rectifier segments are connected between the inner wall of the duct body and the outer wall of the support base.

6. The ducted fan according to claim 5, characterized in that, The rectifier blade is an NACA0012 airfoil.

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