Bionic curved zigzag ducted rotor wing based on owl wings

Abstract

The invention relates to the field of propellers or rotors for airplanes, in particular to a bionic curved zigzag ducted rotor based on owl wings. A bionic curved zigzag ducted rotor wing based on an owl wing comprises a ducted body (1), a support (2) and a rotating shaft (3), the outer end of the support (2) is fixed on the inner side wall of the ducted body (1), the rotating shaft (3) is rotatably arranged at the center of the support (2), the bionic curved zigzag ducted rotor wing is characterized by further comprising at least two rotor wings (4), the rear ends of the rotor wings (4) are fixed on the rotating shaft (3), and the rotor wings (4) are evenly distributed around the rotating shaft (3). Namely, the connecting lines of the outer end points of all the rotor wings (4) form a line segment or a regular polygon with the rotating shaft (3) as the center, gaps are reserved between the front ends of the rotor wings (4) and the inner side wall of the duct body (1), and sawteeth (41) are arranged on the rear edges of the rotor wings (4). The pneumatic performance is excellent, and noise is reduced.

Description

Technical Field

[0001] The 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 is a flying car that wraps the propeller and power unit inside a ducted casing with a certain thickness and shape in the cross section. Due to the design of the duct, the rotor has a good noise suppression effect, but its ability to suppress low-frequency noise is relatively weak, and the increase in lift level requirements caused by the addition of the duct still needs to be further resolved. The main sources of noise when a ducted flying car is working are three parts, namely the noise generated when the rotor rotates, the monopole and dipole sound sources formed when the blades rotate at high speed, and the jet noise generated by the impact and shear of the surrounding still air by the tail flow emitted from the bottom of the duct. The existence of the duct has a certain blocking effect on the noise, so turbulent noise has become the main noise source of the entire flying car. By optimizing and adjusting the structure of the shear layer, it can play a role in adjusting the generation and development of turbulence, thereby effectively controlling the turbulent characteristics of the velocity shear layer, thereby reducing the 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, indirectly leading to the generation of noise. Therefore, it is also worthy of attention to study how to improve the lift level at the same speed by changing the structure of the ducted rotor.

[0003] The main means of rotor noise reduction include the modification of the rotor structure. Introducing bionic serrations and other designs on ducted rotors can effectively reduce noise levels and increase lift levels, but there is currently no research and measures on noise reduction using bionic serrations for ducted rotors. Existing research on rotor noise reduction mainly focuses on the serration of ordinary rotor blades. For example, Wang Bing used three biological characteristics of owls (trailing edge serration structure, leading edge protrusion structure, and wing undersurface texture structure) to improve the noise reduction of UAV rotors, but the application of these three separately only has a certain effect on noise reduction or lift enhancement, and cannot take into account both noise reduction and lift improvement at the same time. Yang Chenghao et al. added trailing edge serration structures of different heights to the upstream and downstream static blades of the engine turbine blades, and verified them using numerical simulation. The trailing edge serrations will generate microjets at the root of the teeth to reduce the impact of the reverse jet and weaken the unsteady interference effect, reducing 8.7dB and 11.8dB at 1BPF and 2BPF respectively, reducing noise while improving aerodynamic performance. However, the leading edge of the downstream blade will be affected by the adverse pressure gradient and the reverse jet, which will increase the noise, resulting in a small improvement in the overall noise level. Qu Wei constructed the serrations by incising the trailing edge of the blade and designed six serrations with different aspect ratios. The six bionic blades at the critical angle of attack were simulated and calculated by the numerical analysis method of large eddy simulation (LES), but no separate research was conducted on ducted rotors. Whether it still has a good noise reduction level under different working environments needs 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 sawtooth ducted rotor based on owl wings.

[0005] The present invention achieves the purpose of the invention through the following technical solutions: A bionic curved sawtooth ducted rotor based on owl wings, comprising a ducted body, a bracket and a rotating shaft, wherein the ducted body is annular, the outer end of the bracket is fixed to the inner side 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 through a bearing, wherein the ducted body and the bracket are annular, the outer end of the bracket is fixed to the inner side 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 through a bearing, and the ducted rotor is characterized in that the ducted rotor further comprises at least two rotors, 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.

[0006] Furthermore, the duct body includes a rear lip and a front cone, the rear lip is a rotating shell whose generatrix is ​​an arc, the front cone is a truncated cone shell, and the front end surface of the rear lip and the large circular end surface of the front cone are smoothly connected; The bracket is star-shaped, and the connecting lines of 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 star shape, which can provide a certain lift for the aircraft when taking off, thereby reducing the load on the rotor and improving the overall efficiency.

[0007] Further, the bracket is cross-shaped; The number of rotors is an even number, and the rear end points of every two rotors overlap and are connected to each other, and the line connecting the two front end points passes through the overlapped rear end points, so that the overlapped rear end points serve as the midpoint of the line connecting the two front end points.

[0008] 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°; 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; 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.

[0009] Furthermore, 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.

[0010] Furthermore, 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; 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; The tooth width b of the sawtooth shall not be less than three times the tooth root spacing d1 of the sawtooth, b shall not be greater than 1mm, d1 shall not be less than 0.1mm, the tooth tip spacing d2 of the sawtooth shall not be less than four times d1, the tooth height h of the sawtooth shall not be greater than 4mm, and the tooth thickness t of the sawtooth shall not be less than 3mm; The average chord length L of the rotor is the ratio of the rotor surface area to the wingspan, and is measured in mm. The maximum chord length of the rotor is taken at 0.8R from the outer end of the rotor, which is approximately 25 mm.

[0011] Furthermore, The profile of the sawtooth is fitted using a bionic curve, and the analytical formula for 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).

[0012] The present invention has the following beneficial effects: The present invention adopts bionic curves to design the serrated trailing edge and front of the ducted rotor of the flying car. In the design of the trailing edge structure of the rotor, it is designed to be a bionic owl wing serrated trailing edge structure. Through the bionic serrated trailing edge, the vortex structure downstream of the flow is further improved, and the generation and radiation of the airfoil aerodynamic noise are reduced, especially in the low-frequency band where ordinary ducted rotors perform poorly. The noise is significantly suppressed; in the leading edge design of the airfoil, a leading edge bionic serrated structure is designed. The leading edge serrations 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, and also improve its lift level.

[0013] The coupled serration structure of the present invention combines the noise reduction characteristics of the leading and trailing edge serrations of a single structure on the rotor, achieving a stronger noise reduction effect than the simple superposition of the leading and trailing edges. The reasonable design of the leading and trailing edge serrations makes the destructive interference effect of sound waves more significant, especially for the suppression of medium and low frequency discrete noise within a frequency of 2kHz. In addition, the leading and trailing edge serrations coordinately control the combing of the airflow and more accurately guide the flow direction, thereby effectively reducing the resistance borne by the rotor and improving aerodynamic efficiency.

[0014] Compared with traditional ducted flying cars, the present invention is quieter when flying, more suitable for flying in highly sound-sensitive areas such as cities, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a top view of the present invention, Figure 2 is an axonometric view of the present invention, Figure 3 is a front view of the duct body in the present invention, Figure 4 is an axonometric view of the rotor in the present invention, Figure 5 is a front view of the rotor in the present invention, Figure 6 is a top view of the rotor in the present invention, Figure 7 is an axonometric view of the sawtooth in the present invention, Figure 8 is a front view of the sawtooth in the present invention, Fig. 9 It is the function image of the sawtooth in the present invention. DETAILED DESCRIPTION

[0016] The present invention is further illustrated by the following specific examples.

[0017] Example 1 A bionic curved sawtooth ducted rotor based on owl wings, comprising a ducted body 1, a bracket 2, a rotating shaft 3 and six rotors 4, such as Figures 1 to 8 As shown, the specific structure is: The duct body 1 is annular, the outer end of the bracket 2 is fixed on the inner wall of the duct body 1, the central axes of the duct 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 through a bearing; The rear end of the rotor 4 is fixed on the rotating shaft 3, and the rotors 4 are evenly distributed around the rotating shaft 3, that is, the connecting line of the outer end points of the rotors 4 forms a regular hexagon with the rotating shaft 3 as the center, and a gap is left between the front end of the rotor 4 and the inner wall of the duct body 1, and the leading edge and the trailing edge of the rotor 4 are provided with saw teeth 41; The rear end points 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 end points, so that the overlapped rear end points serve as the midpoint of the line connecting the two front end points; In this embodiment: 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 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 cross-shaped, and the connecting lines of 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.

[0018] In this embodiment: 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°; 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.

[0019] In this embodiment: 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 wingspan of rotor 4, the average thickness at 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.

[0020] In this embodiment: The distribution position of the sawtooth 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 sawtooth 41 on the trailing edge of the rotor 4 is from 0.6R to 0.95R of the outer end of the rotor 4; 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 spacing d1 of the sawtooth 41, b is 1mm, d1 is 0.1mm, the tooth tip spacing d2 of the sawtooth 4 is not less than four times d1, the tooth height h of the sawtooth 41 is 4mm, and the tooth thickness t of the sawtooth 41 is 3mm; 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.

[0021] In this embodiment: The profile of the sawtooth 41 is fitted by 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), The function graph of formula (I) is as follows Fig. 9 shown.

[0022] When the present 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 figure, S1 is the small circular end face of the front cone 12, S2 is the large circular end face of the front cone, S3 is the front end face of the rear lip 11, and S4 is the rear end face of the rear lip. The noise generated when the rotor 4 rotates is attenuated due to the obstruction of the duct 1. Due to the presence of the sawtooth 41 at the trailing edge of the rotor 4, the downstream vortex system is improved, which plays a good role in noise reduction.

[0023] Inspired by the feather structure of owl wings, combined with the theoretical basis of bionics, this embodiment designs and manufactures the sawtooth structure of the trailing edge of the rotor with a bionic curve according to the actual requirements of the ducted rotor of the flying car, and debugs the parameter combination through experiments. The trailing edge sawtooth structure effectively suppresses the transformation of laminar flow to turbulent flow. Each individual sawtooth structure is equivalent to a vortex generator. The sawtooth can generate a number of corresponding small vortices. While increasing the momentum of the vortex, it increases its adhesion to delay the separation of the airflow, which can well improve the distribution of turbulence on the suction surface of the rotor blade, thereby achieving the purpose of effectively suppressing noise. At the same time, the sawtooth gap acts as a filter for sound waves, so that after the sound waves are absorbed and scattered multiple times, the noise of a specific frequency is effectively suppressed, and the energy is greatly attenuated. Combined with the active noise reduction principle technology, the rotor attitude is changed in real time, and the noise is offset by the interference effect of sound waves to achieve noise reduction. Experiments have shown that compared with ordinary ducted rotors, the blades and combined rotors with the bionic structure described in this experiment can effectively suppress the noise generated during takeoff and landing of flying cars under the same flight conditions. 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 flow 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), wherein: It also includes at least two rotors (4), The rear end of the rotor (4) is fixed on the rotating shaft (3), and the rotors (4) are evenly distributed around the rotating shaft (3), that is, the connecting line of the outer end points of each rotor (4) forms a line segment or a regular polygon with the rotating shaft (3) as the center, 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 the trailing edge of the rotor (4) are provided with saw teeth (41).

2. The bionic curved sawtooth ducted rotor based on owl wings as claimed in claim 1, characterized in that: The duct body (1) comprises 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-shaped 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 connecting lines of 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.

3. The bionic curved sawtooth ducted rotor based on owl wings as claimed in claim 2, characterized in that: The support (2) is cross-shaped; The number of the rotors (4) is an even number, and the rear end points 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 end points, so that the overlapped rear end points serve as the midpoint of the line connecting the two front end points.

4. The bionic curved sawtooth ducted rotor based on owl wings as claimed in claim 3 is characterized in that: The radius of the generatrix of the 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 that 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.

5. The bionic curved sawtooth ducted rotor based on owl wings as claimed in claim 4, characterized in that: The maximum thickness of the bracket (2) is 18% of the chord length of the single cross bracket interface, and the diameter of the rotating surface of the rotor (4) is 2.05R.

6. The bionic curved sawtooth ducted rotor based on owl wings as claimed in claim 5, 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 saw teeth (41) are distributed at the leading edge of the rotor (4) from 0.2R to 0.8R of the outer end of the rotor (4), and the saw teeth (41) are distributed at the trailing edge of the rotor (4) from 0.6R to 0.95R of the outer end of the rotor (4); The tooth width b of the sawtooth (41) is not less than three times the tooth root spacing d1 of the sawtooth (41), b is not greater than 1 mm, d1 is not less than 0.1 mm, the tooth tip spacing d2 of the sawtooth (4) is not less than four times d1, the tooth height h of the sawtooth (41) is not greater than 4 mm, and the tooth thickness t of the sawtooth (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 25 mm.

7. The bionic curved sawtooth ducted rotor based on owl wings as claimed in claim 6, 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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