Ducted rotor for vertical take-off and landing aircraft

Abstract

The present invention relates to the field of propellers or rotors for aircraft, and specifically to a ducted rotor for vertical take-off and landing aircraft. A ducted rotor for vertical take-off and landing aircraft comprises a duct body (1), a bracket (2) and a rotating shaft (3), wherein the outer end of the bracket (2) is fixed on the inner side wall of the duct body (1), and the rotating shaft (3) is rotatably arranged at the center of the bracket (2), and is characterized in that: it also comprises at least two rotors (4), the rear end of the rotor (4) is fixed on the rotating shaft (3), and each rotor (4) is 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, and 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 present invention has excellent aerodynamic performance and reduces noise.

Description

Technical Field

[0001] The invention relates to the field of propellers or rotors for aircraft, in particular to a ducted rotor for vertical take-off and landing aircraft. 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 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, the three biological characteristics of owls (trailing edge serration structure, leading edge protrusion structure, and wing undersurface texture structure) are used 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, increasing noise, resulting in a small improvement in the overall noise level. Qu Wei constructed serrations on the trailing edge of the blade by incising, 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 ducted rotor for a vertical take-off and landing aircraft.

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

[0006] A ducted rotor for a vertical take-off and landing aircraft comprises a duct body, a bracket and a rotating shaft. The duct body is annular, the outer end of the bracket is fixed to the inner side wall of the duct body, the central axes of the duct body and the bracket coincide with each other, and the rotating shaft is rotatably arranged at the center of the bracket through a bearing. The invention is characterized in that: it also comprises at least two rotors,

[0007] The rear end of the rotor is fixed on the rotating shaft, and a top cover is also installed on the rotating shaft to fix the rotor. The rotors are 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 trailing edge of the rotor is 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, 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;

[0009] 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.

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

[0011] 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.

[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] 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.

[0016] 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;

[0017] Assume that the length of the rotor is R, the outer end of the sawtooth is 0.05R away from the outer end of the rotor, the inner end of the sawtooth is 0.6R away from the inner end of the rotor, the tooth height h of the sawtooth is not greater than 4mm, the tooth width b of the sawtooth is not greater than 3mm, the tooth gap d of the sawtooth is not greater than 0.1mm, and the tooth thickness h of the sawtooth is not less than 3mm.

[0018] The ducted rotor for a vertical take-off and landing aircraft is characterized by:

[0019] Divide the rotor into five equal parts along its length:

[0020] From the outer end of the rotor to No sawtooth is set at R;

[0021] since R to The sawtooth set at R is determined by formula (I):

[0022] y=2.6415x4 -2.8185e -6 x 2 +2.02726e -9 x-4.17e -13 ——(I);

[0023] since R to The sawtooth set at R is determined according to formula (II):

[0024] y=3.0095x 4 -2.0496e -6 x 2 +1.4094e -9 x-3.04e -13 ——(II);

[0025] since R to The sawtooth set at R is determined according to formula (III):

[0026] y=3.416x 4 -2.9741e -6 x 2 +2.2276e -9 x-5e -13 ——(III);

[0027] since The sawtooth set at R to R is determined by formula (IV):

[0028] y=3.2615x 4 +4.6711e -9 x-7.63e -13 ——(IV);

[0029] In formula (I) to (IV):

[0030] x: ranges from 0 to tooth height h, representing the ordinate of each point on a single sawtooth bionic curve,

[0031] y: represents half of the tooth width corresponding to the height x on a single sawtooth bionic curve;

[0032] Symmetrically shape the curve about the x-axis to obtain the specific two-dimensional shape of the sawtooth;

[0033] Sawtooth High The edge curve at R~R is determined according to formula (V):

[0034] H(t)=2.8174t 4 -3.45t 3 +8.9521t 2-9.677——(V);

[0035] In formula (V):

[0036] t: the coordinate of any point on the rotor trailing edge with the rotor trailing edge root as the origin,

[0037] H(t): Sawtooth height changes with different lengths from the outer end of the rotor.

[0038] The ducted rotor structure of the present invention is a multi-rotor combination structure, each rotor has the same structure and parameters, and by providing a bionic sawtooth structure at the trailing edge of the rotor, the noise can be effectively reduced and the aerodynamic performance of the rotor can be improved.

[0039] When the present invention is used, the airflow flows in from the small circular end face of the front cone of the duct body, 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, the front end face of the rear lip, and the rear end face of the rear lip in sequence. The noise generated when the rotor rotates is attenuated due to the obstruction of the duct body, and due to the presence of the sawtooth 41 at the rear edge of the rotor, the downstream vortex system is improved, which plays a good role in noise reduction.

[0040] The present invention combines the characteristic part of the ducted vertical take-off and landing aircraft, the ducted body, and the specially designed rotor. Considering the parameters such as the airfoil thickness, the starting position of the rotor taper, the taper ratio, the starting position of the downward deflection, and the downward deflection angle, the parameters that generate the least noise are determined according to the simulated sound pressure level results. At the same time, according to the special structure of the owl's wings, the bionics is used to design a serrated structure at the trailing edge of the airfoil. The trailing edge serrations can reduce noise by changing the flow distribution and reducing turbulence. In addition, it also delays the separation of the flow at the trailing edge through the interaction of microjets and vortices, thereby reducing the scale of the separation bubble and the shedding vortex, and further weakening the noise radiation. At the same time, acoustic tuning noise reduction is considered. By designing the sawtooth bionic curve, the frequency range of the noise is suppressed to the greatest extent, the natural frequency of the blade is changed, and the noise amplification under the resonance condition is avoided. The sawtooth gap acts as a filter for the sound wave, so that the sound wave undergoes more absorption and scattering, resulting in greater attenuation. The active noise reduction principle technology is applied, and through the layout and shape of the rotor, the interference effect of the sound wave is utilized to make the noise sound waves cancel each other in space, thereby achieving noise reduction. In addition, the designed rotor is installed on a twistable base, allowing the rotor angle to be adjusted in real time during flight to adapt to different flight conditions, ultimately maintaining a flight attitude with minimal resistance and improving flight efficiency. Compared with aircraft using traditional airfoils, aircraft using the airfoil proposed by the present invention are quieter when flying, can make vertical take-off and landing aircraft generate less noise pollution when flying in cities, and have better aerodynamic performance, and have broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is a top view of the present invention,

[0042] Figure 2 is an axonometric view of the present invention,

[0043] Figure 3 is a front view of the duct body in the present invention,

[0044] Figure 4 is an axonometric diagram of the duct body in the present invention,

[0045] Figure 5 is an axonometric view of the rotor in the present invention,

[0046] Figure 6 is a front view of the rotor in the present invention,

[0047] Figure 7 is a top view of the rotor in the present invention,

[0048] Figure 8 is an axonometric view of the sawtooth in the present invention,

[0049] Fig. 9 is a front view of the sawtooth in the present invention,

[0050] Fig.10 It is the function graph of the sawtooth from 0.2 wing length to 0.2 wing length of the outer end of the rotor in the present invention,

[0051] Fig.11 It is the function graph of the sawtooth from 0.4 wing length to 0.6 wing length of the outer end of the rotor in the present invention,

[0052] Fig.12 It is the function graph of the sawtooth from 0.6 wing length to 0.8 wing length at the outer end of the rotor in the present invention,

[0053] Fig.13 It is the function graph of the sawtooth from the outer end 0.8 wing length to the full wing length of the rotor in the present invention,

[0054] Fig.14 It is the sawtooth edge curve of the rotor in the present invention from 0.2 wing length at the outer end to the full wing length. DETAILED DESCRIPTION

[0055] The present invention is further described below by means of specific examples.

[0056] Example 1

[0057] A ducted rotor for a vertical take-off and landing aircraft comprises a duct body 1, a bracket 2, a rotating shaft 3 and a rotor 4. Figures 1 to 9 As shown, the specific structure is:

[0058] 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;

[0059] The rear end of the rotor 4 is fixed on the rotating shaft 3, and a top cover is also mounted on the rotating shaft 3 to fix the rotor 4. The top cover and the rotating shaft 3 are fixed by threaded connection. The thickness of the top cover is 2 mm. The use of the top cover can further make the rotor 4 have better dynamic balance performance. It is also convenient to use. The entire rotor 4 can be pre-assembled or temporarily assembled. 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. There is a gap between the front end of the rotor 4 and the inner wall of the duct body 1, and the trailing edge of the rotor 4 is provided with serrations 41.

[0060] In this embodiment, Figure 3 As shown: 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, the front cone 12 is a truncated cone shell, and the rear end surface of the rear lip 11 and the large circular end surface of the front cone 12 are smoothly connected;

[0061] 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; 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.

[0062] Specifically, in this embodiment: the bracket 2 is cross-shaped;

[0063] The number of rotors 4 is six, and the rear end points of every 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.

[0064] Assume that the radius of the rear lip 11 is r=60mm, the inner diameter d of the front end surface of the rear lip 11 is 550mm, the inner diameter D of the rear end surface of the rear lip 11 is 600mm, the thickness δ of the duct body 1 does not exceed 12mm, and the cone angle β of the front cone 12 is 10°.

[0065] 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.

[0066] 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.

[0067] like Figure 8 and Fig. 9 As shown: the outer end of the sawtooth 41 is 0.05R away from the outer end of the rotor 4, the inner end of the sawtooth 41 is 0.6R away from the inner end of the rotor 4, the tooth height h of the sawtooth 41 is not greater than 4mm, the tooth width b of the sawtooth 41 is not greater than 3mm, the tooth gap d of the sawtooth 41 is not greater than 0.1mm, and the tooth thickness h of the sawtooth 41 is not less than 3mm.

[0068] Specifically:

[0069] The rotor 4 is evenly divided into five parts along the length direction:

[0070] From the outer end of the rotor 4 to No sawtooth 41 is provided at R;

[0071] since R to The sawtooth 41 provided at R is determined by formula (I):

[0072] y=2.6415x 4 -2.8185e -6 x 2 +2.02726e -9 x-4.17e -13 ——(I);

[0073] since R to The sawtooth 41 set at R is determined according to formula (II):

[0074] y=3.0095x 4 -2.0496e -6 x 2 +1.4094e -9 x-3.04e -13 ——(II);

[0075] since R to The sawtooth 41 set at R is determined according to formula (III):

[0076] y=3.416x 4 -2.9741e -6 x 2 +2.2276e -9 x-5e -13 ——(III);

[0077] since The sawtooth 41 set at R to R is determined according to formula (IV):

[0078] y=3.2615x4 +4.6711e -9 x-7.63e -13 ——(IV);

[0079] In formula (I) to (IV):

[0080] x: takes values ​​from 0 to tooth height h, representing the ordinate of each point on the bionic curve of a single sawtooth 41,

[0081] y: half of the tooth width corresponding to the height x on the bionic curve representing a single sawtooth 41;

[0082] The curve is symmetrical about the x-axis to obtain the specific two-dimensional shape of the sawtooth 41: R to The sawtooth 41 provided at R is as follows Fig.10 shown, since R to The sawtooth 41 provided at R is as follows Fig.11 shown, since R to The sawtooth 41 provided at R is as follows Fig.12 shown, since The saw teeth 41 arranged at R to R are as follows Fig.13 shown.

[0083] Sawtooth 41 teeth height from The edge curve at R~R is determined according to formula (V):

[0084] H(t)=2.8174t 4 -3.45t 3 +8.9521t 2 -9.677——(V);

[0085] In formula (V):

[0086] t: the coordinate of any point on the trailing edge of rotor 4 with the root of the trailing edge of rotor 4 as the origin,

[0087] H(t): The change of the tooth height of the sawtooth 41 with different lengths from the outer end of the rotor 4.

[0088] The tooth height of the sawtooth 41 of the rotor 4 is The edge curve at R~R is as follows Fig.14 shown.

[0089] The average chord length of the rotor 4 is the ratio of the surface area of ​​the rotor 4 to the unit span, and the unit is mm. In this embodiment, the chord length is at 0.8R, which is about 25 mm.

[0090] 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.

[0091] 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 ducted rotor for a vertical take-off and landing aircraft, 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 the rotors (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 rear edge of the rotor (4) is provided with saw teeth (41); 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 line of each outer end point of the bracket (2) forms an inscribed regular polygon of the inner wall of the duct body (1) with the rotating shaft (3) as the center; 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; 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 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.

2. The ducted rotor for a vertical take-off and landing aircraft according to claim 1, characterized in that: The maximum thickness of the bracket (2) is 18% of the chord length section of a single cross bracket interface, and the diameter of the rotating surface of the rotor (4) is 2.05R.

3. The ducted rotor for a vertical take-off and landing aircraft 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 outer end of the sawtooth (41) is 0.05R away from the outer end of the rotor (4), the inner end of the sawtooth (41) is 0.6R away from the inner end of the rotor (4), the tooth height h of the sawtooth (41) is not greater than 4mm, the tooth width b of the sawtooth (41) is not greater than 3mm, the tooth gap d of the sawtooth (41) is not greater than 0.1mm, and the tooth thickness h of the sawtooth (41) is not less than 3mm.

4. The ducted rotor for a vertical take-off and landing aircraft according to claim 3, characterized in that: The rotor (4) is evenly divided into five parts along the length direction: From the outer end of the rotor (4) to No saw teeth (41) are provided; since to The sawtooth (41) provided at the position is determined by formula (I): y=2.6415x 4 -2.8185e -6 x 2 +2.02726e -9 x-4.17e -13 ——(I); since to The sawtooth (41) provided at the position is determined according to formula (II): y=3.0095x 4 -2.0496e -6 x 2 +1.4094e -9 x-3.04e -13 ——(II); since to The sawtooth (41) provided at the position is determined according to formula (III): y=3.416x 4 -2.9741e -6 x 2 +2.2276e -9 x-5e -13 ——(III); since The sawtooth (41) set at R is determined according to formula (IV): y=3.2615x 4 +4.6711e -9 x-7.63e -13 ——(IV); In formula (I) to (IV): x: takes values ​​from 0 to tooth height h, representing the ordinate of each point on the bionic curve of a single sawtooth (41), y: half of the tooth width corresponding to the height x on the bionic curve representing a single sawtooth (41); Symmetrically adjusting the curve about the x-axis, a specific two-dimensional shape of the sawtooth (41) is obtained; Sawtooth (41) tooth height from The edge curve at is determined by formula (V): H(t)=2.8174t 4 -3.45t 3 +8.9521t 2 -9.677——(V); In formula (V): t: coordinates of any point on the trailing edge of the rotor (4) with the root of the trailing edge of the rotor (4) as the origin, H(t): The change of the tooth height of the sawtooth (41) with different lengths from the outer end of the rotor (4).

Images