Bionic curved sawtooth ducted rotor based on owl wings

Abstract

The present invention relates to the field of propellers or rotors for aircraft, and specifically to a bionic curved sawtooth ducted rotor based on owl wings. A bionic curved sawtooth ducted rotor based on owl wings comprises a duct body (1), a bracket (2) and a rotating shaft (3), wherein the outer end of the bracket (2) is fixed to the inner side wall of the duct body (1), and the rotating shaft (3) is rotatably arranged at the center of the bracket (2). The invention is characterized in that it further comprises at least two rotors (4), the rear ends of the rotors (4) are fixed to the rotating shaft (3), and the rotors (4) are evenly distributed around the rotating shaft (3), that is, the line connecting the outer end points of the rotors (4) forms a line segment or a regular polygon centered on the rotating shaft (3), a gap is left between the front end of the rotor (4) and the inner side wall of the duct body (1), and the trailing edge of the rotor (4) is provided with saw teeth (41). The invention has excellent aerodynamic performance and reduces noise.

Description

Technical Field

[0001] The present invention relates to the field of propellers or rotors for aircraft, in particular to a bionic curved sawtooth ducted rotor based on owl wings. Background Art

[0002] A ducted flying car (FAC) encloses the propeller and powerplant within a ducted casing with a defined cross-sectional thickness and shape. While the ducted design provides excellent rotor noise suppression, its relatively weak ability to suppress low-frequency noise and the increased lift requirements associated with the added ducting still require further resolution. The primary noise sources of a ducted flying car during operation are threefold: rotor noise, monopole and dipole noise generated by high-speed blade rotation, and jet noise caused by the impact and shearing of the wake exiting the duct bottom on the surrounding still air. The duct provides a certain degree of noise isolation, making turbulent noise the primary noise source for the entire flying car. Optimizing the shear layer structure can regulate the generation and development of turbulence, effectively controlling the turbulent characteristics of the velocity shear layer and reducing jet noise. At the same time, due to the introduction of the duct, the overall weight of the flying car increases, so the required lift is also increased. Without changing the structure of the ducted rotor, the operating speed of the rotor will increase, which will indirectly lead to the generation of noise. Therefore, research on improving the lift level at the same speed by changing the structure of the ducted rotor is also worthy of attention.

[0003] The primary means of reducing rotor noise involves modifying the rotor structure. Introducing bionic serrations on ducted rotors can effectively reduce noise levels and increase lift levels, but there is currently no research or measures specifically targeting the use of bionic serrations on ducted rotors. Existing research on rotor noise reduction primarily focuses on the serration of conventional rotor blades. For example, Wang Bing used three biological characteristics of owls (trailing edge serrations, leading edge protrusions, and textured wing undersides) to improve the noise reduction of UAV rotors. However, these three methods, when applied separately, only have a certain effect on either noise reduction or lift enhancement, and cannot simultaneously achieve both noise reduction and lift enhancement. Yang Chenghao et al. added trailing edge serrations of varying heights to the upstream stator blades of an engine turbine blade and verified this using numerical simulations. Trailing-edge serrations generate microjets at the tooth root to reduce the impact of the back jet and weaken the unsteady interference effect, reducing noise by 8.7dB and 11.8dB at 1BPF and 2BPF, respectively. This improves aerodynamic performance while reducing noise. However, the downstream blade leading edge is affected by both the adverse pressure gradient and the back jet, increasing noise and resulting in a minimal improvement in overall noise levels. Qu Wei constructed serrations on the trailing edge of the blade using an inscribed method and designed six serrations with different aspect ratios. He simulated the six bionic blades at critical angles of attack using large eddy simulation (LES) numerical analysis. However, no separate research was conducted on ducted rotors. Whether good noise reduction levels are still achieved under different operating conditions requires further experimental verification. Summary of the Invention

[0004] In order to overcome the defects of the prior art and provide an aircraft rotor with excellent aerodynamic performance and reduced noise, the present invention discloses a bionic curved serrated ducted rotor based on owl wings.

[0005] The present invention achieves the purpose of the invention through the following technical solutions:

[0006] A bionic curved sawtooth ducted rotor based on an owl's wing comprises a ducted body, a bracket and a rotating shaft. The ducted body is annular, the outer end of the bracket is fixed to the inner wall of the ducted body, the central axes of the ducted body and the bracket coincide with each other, and the rotating shaft is rotatably arranged at the center of the bracket via a bearing. The invention is characterized in that it also comprises at least two rotor blades.

[0007] The rear end of the rotor is fixed on the rotating shaft, and each rotor is evenly distributed around the rotating shaft, that is, the line connecting the outer end points of each rotor forms a line segment or regular polygon with the rotating shaft as the center. There is a gap between the front end of the rotor and the inner wall of the duct body, and the leading edge and trailing edge of the rotor are provided with serrations.

[0008] Furthermore, the duct body includes a rear lip and a front cone, the rear lip is a rotating shell whose generatrix is ​​an arc, and the front cone is a truncated cone-shaped shell, and the front end surface of the rear lip and the large circular end surface of the front cone are smoothly connected;

[0009] The bracket is star-shaped, and the lines connecting the outer end points of the bracket form an inscribed regular polygon of the inner wall of the duct with the rotating shaft as the center; the bracket adopts an airfoil-shaped star shape, which can provide a certain lift for the aircraft when taking off, thereby reducing the load on the rotor and improving overall efficiency.

[0010] Furthermore, the bracket is cross-shaped;

[0011] The number of rotors is an even number, and the rear endpoints of every two rotors coincide with each other and are connected, and the line connecting the two front end points passes through the coincident rear endpoints, so that the coincident rear endpoints serve as the midpoint of the line connecting the two front end points.

[0012] Furthermore, assuming that the radius of the rear lip generatrix is ​​r, the inner diameter d of the front end surface of the rear lip is 9r to 9.5r, the inner diameter D of the rear end surface of the rear lip is 10r to 11r, the thickness δ of the duct body does not exceed 0.2r, and the cone angle β of the front cone is 5° to 10°;

[0013] The maximum thickness of the stent is 12% to 20% of the side length of the square formed by the lines connecting the four vertices of the stent;

[0014] Assuming the length of the rotor is R, the diameter of the rotor rotating surface is 2.1R, the average chord length of the rotor is 0.2R, which is the ratio of the surface area of ​​a single blade to the rotor span, and the average thickness of the rear end of the rotor is 0.04R.

[0015] Further,

[0016] The maximum thickness of the bracket is 18% of the chord length of a single cross bracket interface, and the diameter of the rotor rotating surface is 2.05R.

[0017] Further,

[0018] The starting position of the rotor taper is 0.7R from the outer end of the rotor, and the rotor taper ratio is 0.7;

[0019] The distribution position of the saw teeth on the leading edge of the rotor is from 0.2R to 0.8R of the outer end of the rotor, and the distribution position of the saw teeth on the trailing edge of the rotor is from 0.6R to 0.95R of the outer end of the rotor.

[0020] The tooth width b of the saw teeth shall not be less than three times the tooth root spacing d1 of the saw teeth, b shall not be greater than 1mm, d1 shall not be less than 0.1mm, the tooth tip spacing d2 of the saw teeth shall not be less than four times d1, the tooth height h of the saw teeth shall not be greater than 4mm, and the tooth thickness t of the saw teeth shall not be less than 3mm;

[0021] The average chord length L of the rotor is the ratio of the rotor surface area to the wingspan, measured in mm. The maximum chord length of the rotor is taken at 0.8R from the outer end of the rotor, which is about 25mm.

[0022] Further,

[0023] The profile of the sawtooth is fitted using a bionic curve, and the analytical formula for the fitting is shown in formula (I):

[0024] y=-5e -11 x 4 +2.2276e -7 x 3 -2.9741e -4 x 2 +341.6——(I).

[0025] The present invention has the following beneficial effects:

[0026] The present invention uses bionic curves to design the serrated trailing edge and leading edge of the ducted rotor of the flying car. In the design of the rotor's trailing edge structure, it is designed to be a bionic serrated trailing edge structure of an owl's wing. The bionic serrated trailing edge further improves the vortex structure downstream of the flow, reduces the generation and radiation of the airfoil aerodynamic noise, and significantly suppresses noise in the low-frequency band where ordinary ducted rotors perform poorly. In the design of the leading edge of the airfoil, a bionic serrated leading edge structure is designed. The serrations on the leading edge effectively improve the pressure distribution at the leading edge of the rotor and the attachment state of the airflow on the rotor surface. These measures have a significant suppressive effect on the noise of the ducted flying car, while also improving its lift level.

[0027] The coupled serration structure of the present invention combines the noise reduction properties of a single leading and trailing edge serration structure on the rotor, achieving a stronger noise reduction effect than a simple superposition of leading and trailing edges. Through the rational design of the leading and trailing edge serrations, the destructive interference effect of sound waves is more significant, especially for the suppression of low- and medium-frequency discrete noise within a frequency of 2kHz. Furthermore, the leading and trailing edge serrations coordinately control and comb the airflow, more accurately guiding the flow direction, thereby effectively reducing the drag on the rotor and improving aerodynamic efficiency.

[0028] Compared with traditional ducted flying cars, the present invention is quieter during flight and more suitable for flying in high-sound-sensitive areas such as cities, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a top view of the present invention,

[0030] Figure 2 is an axonometric drawing of the present invention,

[0031] Figure 3 This is the main view of the duct body in the present invention,

[0032] Figure 4 is an axonometric view of the rotor in the present invention,

[0033] Figure 5is a front view of the rotor in the present invention,

[0034] Figure 6 is a top view of the rotor in the present invention,

[0035] Figure 7 is an axonometric view of the sawtooth in the present invention,

[0036] Figure 8 It is the front view of the sawtooth in the present invention,

[0037] Figure 9 It is the function image of the sawtooth in the present invention. DETAILED DESCRIPTION

[0038] The present invention is further illustrated below by means of specific examples.

[0039] Example 1

[0040] A bionic curved sawtooth ducted rotor based on owl wings, comprising a ducted body 1, a bracket 2, a rotating shaft 3 and six rotor blades 4, such as Figures 1 to 8 As shown, the specific structure is:

[0041] The duct body 1 is annular, and the outer end of the bracket 2 is fixed to the inner wall of the duct body 1. The central axes of the duct body 1 and the bracket 2 coincide with each other. The rotating shaft 3 is rotatably provided at the center of the bracket 2 via a bearing.

[0042] The rear end of the rotor 4 is fixed to the rotating shaft 3. The rotors 4 are evenly distributed around the rotating shaft 3. That is, the line connecting the outer end points of the rotors 4 forms a regular hexagon centered on the rotating shaft 3. A gap is left between the front end of the rotor 4 and the inner side wall of the duct body 1. The leading and trailing edges of the rotors 4 are provided with serrations 41.

[0043] The rear end points of each two rotor blades 4 are connected to each other and the line connecting the two front end points passes through the coincident rear end point, so that the coincident rear end point serves as the midpoint of the line connecting the two front end points;

[0044] In this embodiment:

[0045] As shown in the figure, the duct body 1 includes a rear lip 11 and a front cone 12. The rear lip 11 is a rotating shell with an arc generatrix, and the front cone 12 is a truncated cone-shaped shell. The front end surface of the rear lip 11 and the large circular end surface of the front cone 12 are smoothly connected.

[0046] The bracket 2 is cross-shaped, and the lines connecting the outer end points of the bracket 2 form an inscribed square of the inner wall of the duct body 1 with the rotating shaft 3 as the center; the bracket 2 adopts an airfoil star shape, which can provide a certain lift for the aircraft when taking off, thereby reducing the load of the rotor 4 and improving the overall efficiency.

[0047] In this embodiment:

[0048] Assume that the radius of the rear lip 11 is r = 60 mm, the inner diameter d of the front end surface of the rear lip 11 is 550 mm, the inner diameter D of the rear end surface of the rear lip 11 is 600 mm, the thickness δ of the duct body 1 does not exceed 12 mm, and the cone angle β of the front cone 12 is 10°;

[0049] The maximum thickness of the bracket 2 is 12% to 20% of the side length of the square formed by the lines connecting the four vertices of the bracket 2 (ie, the chord length of the cross-shaped bracket 2 ), and is 18% in this embodiment.

[0050] In this embodiment:

[0051] Assuming that the length of rotor 4 is R=250mm, the diameter of the rotating surface of rotor 4 is 2.05R, the average chord length of rotor 4 is 0.2R, which is the ratio of the surface area of ​​a single blade to the span of rotor 4, the average thickness of the rear end of rotor 4 is 0.04R, the starting position of the taper of rotor 4 is 0.7R from the outer end of rotor 4, and the taper ratio of rotor 4 is 0.7.

[0052] In this embodiment:

[0053] The serrations 41 are distributed on the leading edge of the rotor 4 from 0.2R to 0.8R of the outer end of the rotor 4, and the serrations 41 are distributed on the trailing edge of the rotor 4 from 0.6R to 0.95R of the outer end of the rotor 4.

[0054] like Figure 7 and Figure 8 As shown: the tooth width b of the sawtooth 41 is not less than three times the tooth root distance d1 of the sawtooth 41, b is 1 mm, d1 is 0.1 mm, the tooth tip distance d2 of the sawtooth 4 is not less than four times d1, the tooth height h of the sawtooth 41 is 4 mm, and the tooth thickness t of the sawtooth 41 is 3 mm;

[0055] The average chord length L of the rotor 4 is the ratio of the surface area of ​​the rotor 4 to the wingspan, and the unit is mm. The maximum chord length of the rotor 4 is taken at 0.8R from the outer end of the rotor 4, which is about 25 mm.

[0056] In this embodiment:

[0057] The profile of the sawtooth 41 is fitted using a bionic curve, and the analytical expression of the fitting is shown in formula (I):

[0058] y=-5e -11 x 4 +2.2276e -7 x 3 -2.9741e -4 x 2 +341.6——(I),

[0059] The function graph of formula (I) is as follows Figure 9 shown.

[0060] When this embodiment is used, the airflow flows in from the small circular end face of the front cone 12 of the duct body 1, and the rotating rotor 4 accelerates the airflow and pushes it backward, and then flows out through the large circular end face of the front cone 12, the front end face of the rear lip 11, and the rear end face of the rear lip 11 in sequence. Figure 3 In the diagram, S1 is the small circular end surface of nose cone 12, S2 is the large circular end surface of nose cone 12, S3 is the front end surface of rear lip 11, and S4 is the rear end surface of rear lip 11. The noise generated by rotor 4 during rotation is attenuated by the obstruction of duct 1. The presence of serrations 41 at the trailing edge of rotor 4 improves the downstream vortex system, effectively reducing noise.

[0061] Inspired by the feather structure of owl wings and incorporating the theoretical basis of bionics, this embodiment designed and fabricated a bionic curved serrated structure on the rotor's trailing edge, based on the practical requirements of a ducted rotor for a flying car. The parameter combination was then adjusted through experiments. The trailing edge serrations effectively inhibit the transition from laminar to turbulent flow. Each individual serration acts as a vortex generator, generating a corresponding number of small vortices. This increases vortex momentum while also enhancing its adhesion, thereby delaying airflow separation. This significantly improves the distribution of turbulence on the rotor blade's suction surface, effectively suppressing noise. Furthermore, the serrated gaps act as acoustic filters, effectively suppressing noise of specific frequencies after multiple absorption and scattering, resulting in significant energy attenuation. Combined with active noise reduction technology, the rotor's attitude is adjusted in real time, utilizing the acoustic interference effect to cancel out noise and achieve noise reduction. Experiments have demonstrated that, compared to conventional ducted rotors, the blades and combined rotors employing this novel bionic structure, under the same flight conditions, can effectively suppress the noise generated during takeoff and landing of a flying car. The ducted rotor of this embodiment is also portable. In addition to being used in flying cars, it can also be used in other rotating machinery that requires noise reduction, such as fan blades, axial fans, etc., and can effectively reduce aerodynamic noise.

Claims

1. A bionic curved sawtooth ducted rotor based on an owl's wing, comprising a ducted body (1), a bracket (2) and a rotating shaft (3), wherein the ducted body (1) is annular, the outer end of the bracket (2) is fixed to the inner side wall of the ducted body (1), the central axes of the ducted body (1) and the bracket (2) coincide with each other, and the rotating shaft (3) is rotatably arranged at the center of the bracket (2), and is characterized by: It also includes at least two rotors (4), The rear end of the rotor (4) is fixed to the rotating shaft (3), and the rotors (4) are evenly distributed around the rotating shaft (3), that is, the line connecting the outer end points of each rotor (4) forms a line segment or a regular polygon centered on the rotating shaft (3), a gap is left between the front end of the rotor (4) and the inner side wall of the duct body (1), and the leading edge and trailing edge of the rotor (4) are provided with serrations (41); The duct body (1) includes a rear lip (11) and a front cone (12), wherein the rear lip (11) is a rotating shell whose generatrix is ​​an arc, and the front cone (12) is a truncated cone shell, and the front end surface of the rear lip (11) and the large circular end surface of the front cone (12) are smoothly connected; The bracket (2) is star-shaped, and the lines connecting the outer end points of the bracket (2) form an inscribed regular polygon of the inner wall of the duct body (1) with the rotating shaft (3) as the center; The bracket (2) is cross-shaped, the number of the rotors (4) is an even number, the rear endpoints of each two rotors (4) overlap and are connected to each other, and the line connecting the two front end points passes through the overlapped rear endpoints, so that the overlapped rear endpoints serve as the midpoint of the line connecting the two front end points; Assuming that the radius of the generatrix of the rear lip (11) is r, the inner diameter d of the front end surface of the rear lip (11) is 9r to 9.5r, the inner diameter D of the rear end surface of the rear lip (11) is 10r to 11r, the thickness δ of the duct body (1) does not exceed 0.2r, and the cone angle β of the front cone (12) is 5° to 10°; The maximum thickness of the bracket (2) is 12% to 20% of the side length of the square formed by connecting the four vertices of the bracket (2); Assuming the length of the rotor (4) is R, the diameter of the rotating surface of the rotor (4) is 2.1R, the average chord length of the rotor (4) is 0.2R, which is the ratio of the surface area of ​​a single blade to the wingspan of the rotor (4), and the average thickness of the rear end of the rotor (4) is 0.04R.

2. The bionic curved sawtooth ducted rotor based on an owl's wing according to claim 1, characterized in that: The maximum thickness of the bracket (2) is 18% of the chord length of a single cross bracket interface, and the diameter of the rotating surface of the rotor (4) is 2.05R.

3. The bionic curved sawtooth ducted rotor based on an owl's wing according to claim 2, characterized in that: The starting position of the tapering of the rotor (4) is 0.7R from the outer end of the rotor (4), and the tapering ratio of the rotor (4) is 0.7; The distribution position of the saw teeth (41) on the leading edge of the rotor (4) is from 0.2R to 0.8R of the outer end of the rotor (4), and the distribution position of the saw teeth (41) on the trailing edge of the rotor (4) is from 0.6R to 0.95R of the outer end of the rotor (4); The tooth width b of the saw teeth (41) is not less than three times the tooth root spacing d1 of the saw teeth (41), b is not greater than 1 mm, d1 is not less than 0.1 mm, the tooth tip spacing d2 of the saw teeth (4) is not less than four times d1, the tooth height h of the saw teeth (41) is not greater than 4 mm, and the tooth thickness t of the saw teeth (41) is not less than 3 mm; The maximum value of the chord length of the rotor (4) is taken at 0.8R from the outer end of the rotor (4), which is 25mm.

4. The bionic curved sawtooth ducted rotor based on an owl's wing according to claim 3, characterized in that: The profile of the sawtooth (41) is fitted using a bionic curve, and the analytical formula of the fitting is shown in formula (I): y=-5e -11 x 4 +2.2276e -7 x 3 -2.9741e -4 x 2 +341.6——(I)。

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