Ducted fan based on bionic structure

Abstract

The invention discloses a ducted fan based on a bionic structure. The ducted fan comprises a driving motor, propellers and a ducted body. The driving motor is used for driving the propeller to rotate; the propeller is arranged in a space enclosed by the duct body; bird-feather-shaped grooves are formed in the inner wall face of the duct body, the multiple sets of bird-feather-shaped grooves are circumferentially arranged around the face wall of the duct body and extend in the axial direction of the duct body, and the positive and negative groove angles of the adjacent bird-feather-shaped grooves are opposite. According to the invention, the bird feather-shaped grooves are introduced into the surface of the duct body, so that the gas flow on the wall surface of the duct body is improved, and the overall operation noise is reduced; and compared with a reference fan, the ducted fan has a good application prospect in the aspect of noise reduction, does not change the original design shape of the section of the duct and the matching relation between the propeller and the duct, and has more modifiability.

Description

Technical Field

[0001] The present invention relates to the technical field of ducted fans, and in particular to a ducted fan based on a bionic structure. Background Art

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

[0003] The ducted fan is mainly composed of a propeller, a ducted casing and a drive motor. It is mainly a fan structure with a hard casing wrapped around the propeller. The casing can not only protect ground personnel from being harmed by the propeller, but also isolate the interference of the harsh external environment on the operation of the propeller to a certain extent. It can also suppress the propeller wingtip vortex and rectify the front flow, 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 serve as a noise reflection surface to isolate the tonal noise and broadband noise caused by the propeller tip vortex shedding, thus achieving a noise shielding effect, which is of great significance for the future operation of eVTOL in low-altitude cities.

[0005] The main difficulty in optimizing the design of ducted fans is to balance thrust performance and noise performance. Previous researchers focused on the airfoil profile of the duct, the shape of the propeller, and the coordination between the duct and the propeller. Since the 1950s, a large number of studies have been carried out based on the above design goals.

[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 an urgent problem to be solved by those skilled in the art. Summary of the invention

[0007] The purpose of the present invention is to provide a ducted fan based on a bionic structure to solve the problem that the noise of the existing ducted fan is difficult to further reduce.

[0008] In order to solve the above technical problems, the present invention provides a ducted fan based on a bionic structure, comprising a drive motor, a propeller and a duct body; the drive motor is used to drive the propeller to rotate; the propeller is arranged in the space enclosed by the duct body; a bird-feather-shaped groove is provided on the inner wall surface of the duct body, and a plurality of groups of the bird-feather-shaped grooves are circumferentially arranged around the surface wall of the duct body, and the plurality of groups of the bird-feather-shaped grooves are all arranged along the axial extension of the duct body, and the groove angles of adjacent bird-feather-shaped grooves are opposite in positive and negative directions.

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

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

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

[0012] In one embodiment, the support frame includes a support seat and a straightening piece; the support seat is arranged at the center of the space enclosed by the duct body, and the drive motor and the propeller are installed on the support seat; a plurality of straightening pieces are connected between the inner wall of the duct body and the outer wall of the support seat.

[0013] In one embodiment, the fairing is a NACA0012 airfoil.

[0014] In one embodiment, in the circumferential direction, the groove angles of adjacent bird-feather-shaped grooves are opposite in positive and negative directions every 10° to 20°.

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

[0016] The beneficial effects of the present invention are as follows:

[0017] The present invention improves the wall gas flow of the duct and reduces the overall operating noise by introducing bird-feather-shaped grooves on the surface of the duct. Moreover, this ducted fan not only has good application prospects in noise reduction compared with its benchmark fan, but also does not change the original duct profile design shape and the matching relationship between the propeller and the duct, and has more modifiability. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solution of the present invention, the drawings required for use in the implementation mode will be briefly introduced below. Obviously, the drawings described below are only some implementation modes of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 It is a schematic diagram of the structure provided by an embodiment of the present invention;

[0020] Figure 2 yes Figure 1 Schematic diagram of the partial cross-sectional structure of the duct body;

[0021] Figure 3 yes Figure 1 Schematic diagram of bird feather shaped groove layout;

[0022] Figure 4 yes Figure 3 A schematic diagram of the enlarged structure of part A;

[0023] Figure 5 yes Figure 1 Schematic diagram of the support frame structure;

[0024] Figure 6 is a schematic diagram of the reference ducted fan structure for the comparison test;

[0025] Figure 7 It is a schematic diagram of the external structure of the bird-feather-shaped groove of the ducted fan for comparison test;

[0026] Figure 8 is the ducted fan OASPL azimuth distribution Figure 1 ;

[0027] Fig. 9 is the ducted fan OASPL azimuth distribution Figure 2 ;

[0028] Fig.10 is the ducted fan OASPL azimuth distribution Figure 3 ;

[0029] Fig.11 is the ducted fan OASPL azimuth distribution Figure 4 ;

[0030] Fig.12 is the ducted fan OASPL azimuth distribution Figure 5 ;

[0031] Fig.13 is the ducted fan OASPL azimuth distribution Figure 6 ;

[0032] Fig.14is the ducted fan OASPL azimuth distribution Figure 7 ;

[0033] Fig.15 is the ducted fan OASPL azimuth distribution Figure 8 ;

[0034] Fig.16 This is the spectrum characteristic curve of the ducted fan at an incoming flow velocity of 20m / s Figure 1 ;

[0035] Fig.17 This is the spectrum characteristic curve of the ducted fan at an incoming flow velocity of 20m / s Figure 2 ;

[0036] Fig.18 This is the spectrum characteristic curve of the ducted fan at an incoming flow velocity of 20m / s Figure 3 ;

[0037] Fig.19 This is the spectrum characteristic curve of the ducted fan at an incoming flow velocity of 20m / s Figure 4 .

[0038] The reference numerals are as follows:

[0039] 10. Driving motor;

[0040] 20. Propeller;

[0041] 30. Duct;

[0042] 40. Bird-feather-shaped grooves;

[0043] 50. Support frame; 51. Support seat; 52. Rectifier. DETAILED DESCRIPTION

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

[0045] The present invention provides a ducted fan based on a bionic structure, wherein a first embodiment of the present invention is Figures 1 to 5 As shown, it includes a driving motor 10, a propeller 20 and a duct 30.

[0046] Regarding the driving motor 10, Figure 1 As shown, in this embodiment, a driving motor 10 is provided to drive the propeller 20 to rotate, so the driving motor 10 can generate a driving force to control the propeller 20 to rotate at a high speed by simply connecting and fixing the rotating shaft of the driving motor 10 to the propeller 20.

[0047] Regarding the propeller 20, Figure 1As shown, in this embodiment, the propeller 20 is arranged in the space enclosed by the duct body 30 to isolate the operation of the propeller 20 from interference by the harsh external environment; and at this time, a wingtip gap is left between the wingtip of the propeller 20 and the inner wall surface of the duct body 30, and the wingtip gap is within 0.5% to 1% of the diameter of the propeller 20. For example, in this embodiment, the wingtip gap is set to 1% of the diameter of the propeller 20.

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

[0049] 1. Ensure that the propulsion efficiency is sufficient. If the wingtip clearance is too small, the airflow velocity gradient between the wingtip of the propeller 20 and the inner wall of the duct 30 will increase, resulting in increased friction resistance and reduced propulsion efficiency. In addition, manufacturing errors or thermal expansion of materials may cause the wingtip of the propeller 20 to contact the inner wall of the duct 30, causing mechanical damage or vibration.

[0050] If the wingtip clearance is too large, the wingtip vortex will be enhanced. For example, when the propeller 20 rotates, the high pressure difference at the wingtip of the propeller 20 will form a strong wingtip vortex, resulting in energy loss. If the wingtip clearance is too large, the duct's vortex suppression effect will be weakened, thereby reducing the propulsion efficiency; and at this time, the duct's guiding function cannot be fully exerted, and the thrust of the propeller 20 may also decrease.

[0051] 2. Reduce aerodynamic noise. If the wingtip clearance is too small, the airflow will be accelerated in the narrow wingtip clearance and form a turbulent boundary layer, generating harsh high-frequency noise. If the wingtip clearance is too large, the unsuppressed wingtip vortex will interact with the inner wall of the duct 30, resulting in an increase in low-frequency vortex noise. Therefore, appropriately reducing the wingtip clearance will suppress the wingtip vortex, thereby reducing the overall noise level.

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

[0053] 4. Improve mechanical reliability. If the wingtip clearance is too small, long-term micro-contact or airflow impact may accelerate fatigue damage to the wingtip of the propeller 20 or the inner wall of the duct 30, and material expansion under high temperature conditions may further reduce the clearance, increasing the risk. If the wingtip clearance is too large, it will cause uneven aerodynamic loads, and uneven flow may cause force fluctuations on the propeller 20, shortening the life of components.

[0054] 5. Reduce processing and maintenance costs. If the wingtip clearance is too small, higher manufacturing precision (such as precision machining or composite material molding) is required, which increases production costs. In addition, frequent checks on clearance changes are required during maintenance to avoid performance degradation due to wear or deformation. If the wingtip clearance is too large, although it can reduce manufacturing and maintenance costs, it may sacrifice aerodynamic efficiency or noise performance.

[0055] 6. Ensure that hovering efficiency can be met, because small gaps can improve hovering efficiency, but the impact of noise and vibration on the sensor needs to be balanced.

[0056] In summary, the size of the wingtip clearance will have many effects on the ducted fan. After a large number of experimental verifications, the present invention found that when the wingtip clearance is within 0.5% to 1% of the diameter of the propeller 20, the best overall performance will be achieved. For example, setting the wingtip clearance to 1% of the diameter of the propeller 20 is a preferred solution.

[0057] It should be noted that in order to realize the installation of the drive motor 10 and the propeller 20, this embodiment adopts Figure 1 and Figure 5 In the arrangement shown, a support frame 50 is provided in the space enclosed by the duct body 30 , the support frame 50 and the duct body 30 are integrally formed, and a driving motor 10 and a propeller 20 are mounted on the support frame 50 .

[0058] Specifically, the support frame 50 at this time includes a support seat 51 and a rectifier 52; the support seat 51 is cylindrical in shape, and the support seat 51 is arranged at the center of the space enclosed by the duct body 30, and the drive motor 10 and the propeller 20 are installed on the support seat 51; multiple rectifiers 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 52 in this embodiment is four pieces, and the four rectifiers 52 are arranged on the four sides of the support seat 51 at equal intervals, so that the support frame 50 as a whole is roughly cross-shaped.

[0059] Since the drive motor 10 is connected and fixed to the propeller 20 , it is only necessary to connect and fix the drive motor 10 to the support seat 51 to achieve installation and fixation of the drive motor 10 and the propeller 20 on the support frame 50 .

[0060] Furthermore, the fairing 52 of this embodiment is a NACA0012 airfoil, and this arrangement has at least the following beneficial effects:

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

[0062] 2. It has the characteristics of low resistance and efficient flow control. For example, its resistance is minimum at zero angle of attack, and its resistance coefficient Cd ≈0.006, which is suitable for scenes that require smooth flow guidance; it can not only reduce turbulence and pressure difference resistance in high-speed flow, but also inhibit airflow separation, such as NACA0012 airfoil at higher Reynolds numbers (Re>1×10 6 )The lower boundary layer is more stable, avoiding premature separation.

[0063] 3. It has performance advantages at high Reynolds numbers and performs better in transonic or high-speed flows. For example, when approaching the speed of sound, the NACA0012 airfoil delays the generation of shock waves and reduces wave drag. In addition, the NACA0012 airfoil also responds faster to airflow disturbances.

[0064] 4. Lightweight structure and easy manufacturing. The thickness of the NACA0012 airfoil reduces weight while ensuring strength, making it more suitable for weight-sensitive applications (such as drones and spacecraft). In addition, the symmetrical design of the NACA0012 airfoil simplifies mold manufacturing (such as injection molding or 3D printing), making it suitable for standardized production and reducing costs.

[0065] 5. It has wide adaptability to angles of attack. For example, although the NACA0012 airfoil is most efficient at zero angle of attack, it can still maintain low resistance and low turbulence within an angle of attack of ±8°. It also has adaptability to complex flow fields and can reduce performance fluctuations in non-uniform incoming flows.

[0066] 6. With low noise characteristics, the NACA0012 airfoil has almost no separation flow at zero angle of attack, thus reducing turbulent pulsation noise.

[0067] Regarding the duct body 30, Figures 1 to 4 As shown, bird-feather-shaped grooves 40 are provided on the inner wall surface of the duct body 30, and multiple groups of bird-feather-shaped grooves 40 are circumferentially arranged around the surface wall of the duct body 30. The multiple groups of bird-feather-shaped grooves 40 are all arranged along the axial extension of the duct body 30, and the groove angles of adjacent bird-feather-shaped grooves 40 are opposite in positive and negative directions, so that the bird-feather-shaped grooves 40 present a periodic distribution structure of upward wedges, downward wedges, and upward wedges, and the appearance at this time is roughly herringbone-shaped.

[0068] For the present invention, the provision of the bird-feather-shaped groove 40 is the core of the entire solution and the key point to reduce noise. Therefore, in order to better reflect the importance of the provision of the bird-feather-shaped groove 40, it will be explained below in conjunction with a specific comparative example.

[0069] This comparative experiment is a noise test of the ducted fan, mainly comparing the reference ducted fan with the NACA0018 airfoil profile (i.e. Figure 6 As shown in the figure, the noise performance of ducted fans (with bird-feather-shaped grooves 40) with three different design parameters at an angle of attack of 0°-15° under incoming flow conditions.

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

[0071]

[0072] Specific test results are as follows Figures 8 to 15 As shown:

[0073] Figure 8 This is the OASPL distribution diagram of the ducted fan with the bird-feather-shaped groove 40 at an attack angle of 0° and an incoming flow of 10m / s from the front.

[0074] Fig. 9 This is the OASPL distribution diagram of the ducted fan with a bird-feather-shaped groove 40 at an attack angle of 0° and an incoming flow of 20m / s from the front.

[0075] Fig.10 It is the OASPL distribution diagram of the ducted fan with the bird-feather-shaped groove 40 at an attack angle of 5° and an incoming flow of 10m / s from the front.

[0076] Fig.11 This is the OASPL distribution diagram of the ducted fan with the bird-feather-shaped groove 40 at an attack angle of 5° and an incoming flow of 20 m / s from the front.

[0077] Fig.12 It is the OASPL distribution diagram of the ducted fan with the bird-feather-shaped groove 40 at an attack angle of 10° and an incoming flow of 10 m / s from the front.

[0078] Fig.13 It is the OASPL distribution diagram of the ducted fan with the bird-feather-shaped groove 40 at an attack angle of 10° and an incoming flow of 20 m / s from the front.

[0079] Fig.14 It is the OASPL distribution diagram of the ducted fan with the bird-feather-shaped groove 40 at an attack angle of 15° and an incoming flow of 10 m / s from the front.

[0080] Fig.15 It is the OASPL distribution diagram of the ducted fan with the bird-feather-shaped groove 40 at an attack angle of 15° and an incoming flow of 20 m / s from the front.

[0081] The results show that, under low flow rate and low angle of attack, the duct with the bird-feather-shaped groove 40 has limited noise reduction effect compared with the reference duct, and may even increase noise in some cases. Under higher flow rate and higher angle of attack, regardless of whether the bird-feather-shaped groove 40 is arranged inside the duct body 30 (i.e. Figure 1shown) or external (i.e. Figure 7 The noise reduction effect is very significant, and in some cases the noise reduction performance is as high as nearly 4dBA. For example, the test results at a flow velocity of 20m / s and an attack angle of 15° are shown in the following table:

[0082]

[0083] It can be seen from the above table that the maximum noise reduction effect occurs at an azimuth angle of 65°, that is, near the duct inlet.

[0084] The frequency spectrum characteristics of the azimuth angle of 45° are analyzed to explore the main frequency band of the groove structure noise reduction. Figures 16 to 19 It can be seen that the attack angles of the bird-feather-shaped groove 40 are 0°, 5°, 10° and 15° respectively. It can be found that the main noise reduction frequency bands of the bird-feather-shaped groove 40 are the fundamental frequency of the propeller 20, that is, 133 Hz; the second is the mid-frequency region near 1000 Hz, which exhibits a strong noise characteristic of the airfoil trailing edge noise. It can be analyzed that the bird-feather-shaped groove 40 improves the overall noise performance by improving the wingtip flow of the propeller 20 inside the ducted fan and the trailing edge noise of the airfoil at the trailing edge of the ducted fan.

[0085] Therefore, the setting parameters of the bird-feather-shaped groove 40 have a crucial influence on the performance of the duct. Therefore, in order to ensure that the ducted fan can meet the design requirements after the bird-feather-shaped groove 40 is set, it is recommended that the groove angles of adjacent bird-feather-shaped grooves 40 are opposite in the circumferential direction every 10° to 20°, and the attack angle of the bird-feather-shaped groove 40 is set to 15° to 20°; for example, Figure 3 As shown in FIG. 1 , this embodiment sets the groove angles of adjacent bird-feather-shaped grooves 40 to be opposite at every 15° interval, and Figure 4 It can be seen that at this time, the groove width of the bird-feather-shaped groove 40 is a, the groove height is b, and the groove angle is α.

[0086] It should also be pointed out that if Figure 2 As shown, in this embodiment, the cross section of the duct body 30 is a NACA0018 airfoil.

[0087] The above is a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A ducted fan based on a bionic structure, characterized in that: Including drive motor, propeller and duct; The driving motor is used to drive the propeller to rotate; The propeller is arranged in the space enclosed by the duct; The inner wall surface of the duct body is provided with bird-feather-shaped grooves, and multiple groups of the bird-feather-shaped grooves are circumferentially arranged around the surface wall of the duct body. The multiple groups of the bird-feather-shaped grooves are all arranged along the axial extension of the duct body, and the groove angles of adjacent bird-feather-shaped grooves are opposite in positive and negative directions.

2. The ducted fan according to claim 1, wherein: A wingtip gap is left between the wingtip of the propeller and the inner wall surface 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, wherein: The cross section of the duct is a NACA0018 airfoil.

4. The ducted fan according to claim 1, wherein: A support frame is provided in the space enclosed by the duct body. The support frame is integrally formed with the duct 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 seat and a rectifier; The support seat is arranged at the center of the space enclosed by the duct body, and the drive motor and the propeller are installed on the support seat; A plurality of the rectifying sheets are connected between the inner wall of the duct body and the outer wall of the supporting seat.

6. The ducted fan according to claim 5, characterized in that: The fairing is a NACA0012 airfoil.

7. The ducted fan according to claim 1, wherein: In the circumferential direction, the groove angles of adjacent bird-feather-shaped grooves are opposite in positive and negative directions every 10° to 20°.

8. The ducted fan according to claim 1, wherein: The attack angle of the bird-feather-shaped groove is 15° to 20°.

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