A heterogeneous coaxial dual-rotor system

Abstract

This invention relates to a coaxial dual-rotor system with heterogeneous upper and lower rotors, belonging to the field of aircraft design technology. It solves the problem in existing coaxial dual-rotor systems where the natural frequencies of the upper and lower rotors are close, leading to resonance amplification of vibration loads and causing helicopter fuselage vibration and ground resonance. The system includes: a coaxially arranged upper and lower rotor, and a rotor hub connecting the upper and lower rotors to the fuselage; an inner sleeve and an outer sleeve arranged within the rotor hub, respectively connected to the upper and lower rotors, enabling the upper and lower rotors to rotate in opposite directions; the inner sleeve and outer sleeve are respectively connected to the aircraft's power system and control system via transmission mechanisms to achieve speed and collective pitch adjustment; wherein the upper and lower rotors have different radii; the number of blades on the upper rotor and the lower rotor is in the range of 2 to 6; the ratio of the vertical distance between the upper and lower rotors along the rotation axis to the radius of the upper rotor is in the range of 0.1 to 1.00.

Description

Technical Field

[0001] This invention relates to the field of aircraft design technology, specifically to a coaxial dual-rotor system with heterogeneous size. Background Technology

[0002] A coaxial twin-rotor helicopter consists of two rotors mounted on the same axis, which act as the lifting surface, thrust surface, and control surface. Compared to conventional helicopters with a single rotor and tail rotor, coaxial twin-rotor helicopters have several advantages: First, they have a greater payload potential. The coaxial twin-rotor generates thrust through the two rotors, allowing for higher lift redundancy within the constraints of helicopter size. Second, they have a more compact structure. When the two rotors rotate in opposite directions, torque balance can be achieved by adjusting the rotor pitch or rotational speed, eliminating the need for a tail rotor. This allows the fuselage structure to be shortened to within the rotor disk area, reducing pitch and yaw inertia, improving handling efficiency and maneuverability, and enhancing wind resistance. Third, they have higher power utilization. The tail rotor-less design avoids tail rotor power consumption, allowing more engine power to be used for thrust generation, improving hovering efficiency; a typical coaxial twin-rotor helicopter's hovering power is only about 80% of that of a conventional helicopter. Therefore, in complex terrain conditions such as urban areas and mountainous regions, coaxial twin-rotor helicopters are more suitable than conventional helicopters for low-altitude operations such as air traffic, logistics distribution, and emergency rescue, and have broad application prospects.

[0003] Several helicopters have been developed based on the coaxial dual-rotor configuration for low-altitude operations in complex terrains such as plateaus, deserts, forests, and islands. In recent years, the coaxial dual-rotor configuration has also been used in the design of electric vertical takeoff and landing (eVTOL) aircraft such as small unmanned helicopters and multi-rotor aircraft.

[0004] The mutual interference between the upper and lower rotors of a coaxial twin-rotor helicopter will lead to serious vibration and noise problems. On the one hand, the periodic staggering and divergence of the blades generate periodic pulsating loads, making the vibration load transmitted to the rotor hub greater than that of a single rotor. Since the upper and lower rotors of existing coaxial twin-rotor helicopters are of the same size and have similar natural frequencies, the superposition of their amplitudes can easily cause resonance, further amplifying the vibration load. Excessive vibration will cause prominent problems such as helicopter fuselage vibration and ground resonance, affecting flight control, weakening mission capabilities, and threatening flight safety. On the other hand, the periodic staggering of the rotor blades also causes pulsating changes in the blade surface pressure, generating aerodynamic noise. In addition, the slipstream of the upper rotor contracts when it reaches the plane of the lower rotor disk, causing the upper rotor tip vortex to collide with the lower rotor blade, generating blade-vortex interference; the tip vortices of the upper and lower rotors further entangle, merge, and distort downstream, generating vortex-vortex interference. Blade-vortex interference and vortex-vortex interference in twin-rotor helicopters become additional noise sources, making coaxial twin-rotor helicopters face more prominent noise problems than conventional single-rotor helicopters.

[0005] Chinese invention patent application, publication number CN109878713A, entitled "Miniature Coaxial Dual-Rotor UAV," discloses a miniature coaxial dual-rotor UAV comprising a coaxial upper rotor, a lower rotor, and a dual-rotor support. The upper and lower rotors are of the same size and each has two blades. Because the upper and lower rotors of this coaxial dual-rotor UAV are of the same size, their natural vibration frequencies are similar. The superposition of their amplitudes causes resonance, further amplifying the vibration load and reducing flight efficiency.

[0006] Chinese utility model patent, publication number CN204507261U, entitled "A Coaxial Co-rotor Multi-rotor Helicopter," discloses a coaxial twin-rotor helicopter, including an aircraft body and main rotors. The main rotors include rotor one and rotor two, wherein rotor one and rotor two are the same size and each has two blades. Therefore, this coaxial twin-rotor helicopter still suffers from the problem that the natural frequencies of rotor one and rotor two are close, and the superposition of amplitudes can cause resonance.

[0007] Therefore, there is a need in this field for a coaxial twin-rotor system that can reduce vibration and noise and has high aerodynamic efficiency. Summary of the Invention

[0008] This invention addresses the prominent vibration and noise problems faced by existing coaxial dual-rotor systems by proposing a coaxial dual-rotor system with heterogeneous upper and lower rotor radii. The different radii of the upper and lower rotors in this system help reduce pressure and thrust fluctuations on the blade surface, thereby achieving vibration and noise reduction.

[0009] According to an embodiment of the present invention, a coaxial dual-rotor system with different sizes is provided for mounting to the fuselage of a helicopter, comprising: an upper rotor and a lower rotor arranged coaxially, and a rotor hub connecting the upper rotor and the lower rotor to the fuselage; an inner sleeve and an outer sleeve are arranged inside the rotor hub and are respectively connected to the upper rotor and the lower rotor to achieve opposite rotation of the upper rotor and the lower rotor; the inner sleeve and the outer sleeve are respectively connected to the power system and the control system of the aircraft via a transmission mechanism to achieve speed and collective pitch adjustment;

[0010] The upper rotor and the lower rotor have different radii;

[0011] The radii of the upper and lower rotors are no greater than 8.0m;

[0012] The number of blades on the upper rotor and the lower rotor ranges from 2 to 6.

[0013] The ratio of the distance between the upper and lower rotors in the vertical direction of the rotation axis to the radius of the upper rotor is in the range of 0.1 to 1.00.

[0014] Optionally, the radius ratio of the lower rotor to the upper rotor is in the range of 0.5 to 2.00; the number of blades on the upper rotor is different from the number of blades on the lower rotor.

[0015] Optionally, the blade twist angle of the upper rotor is different from that of the lower rotor.

[0016] Optionally, the blade twist angle distribution of the upper rotor is as follows:

[0017]

[0018] in, The blade twist angle distribution of the upper rotor. The blade tip twist angle of the upper rotor. Indicates the spanwise position of the rotor blades. The radius of the upper rotor;

[0019] The blade twist angle distribution of the lower rotor is as follows:

[0020]

[0021] in, The blade twist angle distribution of the lower rotor. This refers to the tip twist angle of the lower rotor blade. This indicates the spanwise position of the lower rotor blades. Where is the radius of the lower rotor.

[0022] Optionally, the blade chord length distribution of the upper rotor is different from that of the lower rotor.

[0023] Optionally, the blade chord length distribution of the upper rotor is as follows:

[0024]

[0025] in, The blade chord distribution of the upper rotor. The tip chord of the rotor blades is the length of the rotor blades. The blade root-to-tip ratio of the upper rotor. Indicates the spanwise position of the rotor blades. The radius of the upper rotor;

[0026] The blade chord distribution of the lower rotor is as follows:

[0027]

[0028] in, The blade chord distribution of the lower rotor. The tip chord of the rotor blade is the length of the lower rotor blade. This indicates the spanwise position of the lower rotor blades. Where is the radius of the lower rotor.

[0029] Optionally, the upper rotor has two blades and the lower rotor has three blades;

[0030] The upper rotor has a radius of 0.4m, the lower rotor has a radius of 0.28m, and the ratio of the lower rotor radius to the upper rotor radius is 0.7.

[0031] The vertical distance between the upper and lower rotors along the axis of rotation is 0.12 m;

[0032] The ratio of the distance between the upper and lower rotors in the vertical direction of the rotation axis to the radius of the upper rotor is 0.3.

[0033] Optionally, the upper rotor has blades with a linear chord length distribution, a root-to-tip ratio of 2, and a blade tip chord length of 0.04m;

[0034] The lower rotor has rectangular blades, and the blades are in The chord length in the 0.85 range is 0.04m. The portion exceeding 0.85 has a sharp point; among which, This indicates the spanwise position of the lower rotor blades. This indicates the radius of the lower rotor.

[0035] Optionally, the blades of the upper rotor have a 15° linear negative twist, while the blades of the lower rotor have no twist.

[0036] Optionally, the number of blades on the upper rotor is the same as that on the lower rotor, which is two blades each.

[0037] The upper rotor has a radius of 2m, the lower rotor has a radius of 1.5m, and the ratio of the lower rotor radius to the upper rotor radius is 0.75.

[0038] The vertical distance between the upper and lower rotors along the axis of rotation is 0.3 m;

[0039] Neither the upper nor lower rotor blades twisted;

[0040] Both the upper and lower rotor blades are rectangular;

[0041] The blades of the upper and lower rotors have the same chord length, which is 0.2m.

[0042] Compared with the prior art, the coaxial dual rotor system with different sizes provided by the present invention has at least the following beneficial effects.

[0043] (1) The heterogeneous coaxial dual rotor system of the present invention, by limiting the ratio of the distance between the upper rotor and the lower rotor in the vertical direction (along the direction of the rotation axis) to the radius of the upper rotor to the range of 0.1 to 1.00, can not only avoid the collision of the upper and lower rotor blades, but also avoid the heterogeneous dual rotor system being too large in the vertical direction, thereby reducing flight drag.

[0044] (2) Compared with existing coaxial dual rotor systems with equal upper and lower rotor radii, the coaxial dual rotor system of the present invention has a smaller overlapping area of ​​the upper and lower rotor disks, which can reduce the unsteady fluctuation of rotor thrust and is beneficial to reduce pulse load and vibration level. Furthermore, when used in helicopters with small disk loads, such as helicopters with rotor radius less than 8.0m, it can significantly improve aerodynamic efficiency, reduce aerodynamic noise, and effectively avoid resonance between the fuselage and the upper and lower rotors.

[0045] (3) The coaxial dual rotor system of the present invention with different sizes can reduce the aerodynamic interference between the upper and lower rotors compared with the existing coaxial dual rotors with equal upper and lower rotor radii, which is beneficial to improving the aerodynamic performance of the rotor.

[0046] (4) Compared with existing coaxial dual rotors with equal upper and lower rotor radii, the size heterogeneous coaxial dual rotor system of the present invention reduces the aerodynamic interference between the upper and lower rotors, can reduce the pressure pulsation on the blade surface, and can reduce blade-vortex interference and vortex-vortex interference under certain conditions, which is beneficial to reducing aerodynamic noise.

[0047] (5) The coaxial dual rotor system of the present invention has different shapes and natural frequencies than existing coaxial dual rotors with equal upper and lower rotor radii. This can reduce the superposition of vibration energy and effectively avoid resonance.

[0048] (6) The coaxial dual rotor system of the present invention with different sizes can have different parameters such as the radius of the upper and lower rotors, the number of blades, the twist angle, the planar shape, and the airfoil compared with the existing coaxial dual rotor with equal upper and lower rotor radii, thus expanding the optimization space and performance boundaries. Attached Figure Description

[0049] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the embodiments will be briefly introduced below. The features and advantages of the present invention can be more clearly understood by referring to the accompanying drawings. The accompanying drawings are schematic and should not be construed as limiting the present invention in any way. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0050] Figure 1 This is a schematic diagram of Embodiment 1 of a coaxial dual-rotor system with heterogeneous size according to an embodiment of the present invention.

[0051] Figure 2 Example 1 of the coaxial dual-rotor system with different sizes provided according to an embodiment of the present invention is shown in the thrust-power coefficient curve comparison diagram with an existing coaxial dual-rotor system with the same upper and lower rotors.

[0052] Figure 3 The hovering efficiency-thrust coefficient curves of the heterogeneous coaxial dual-rotor system of Example 1 are compared with those of an existing coaxial dual-rotor system with the same upper and lower rotors.

[0053] Figure 4 The graph shows the unsteady variation curve of the thrust coefficient of the heterogeneous coaxial dual rotor system in Example 1.

[0054] Figure 5 This is a graph showing the unsteady variation of the thrust coefficient of an existing coaxial twin-rotor system with identical upper and lower rotors.

[0055] Figure 6 This is a comparison diagram of the noise level directivity of the heterogeneous coaxial dual-rotor system of Example 1 with that of an existing coaxial dual-rotor system with the same upper and lower rotors.

[0056] Figure 7 A schematic diagram of Embodiment 2 of a heterogeneous coaxial dual rotor system according to an embodiment of the present invention.

[0057] Figure label:

[0058] 1-Uprotor;

[0059] 2-Lower rotor;

[0060] 3-Propeller hub. Detailed Implementation

[0061] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0062] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0063] The following detailed description, with reference to the accompanying drawings, illustrates a heterogeneous coaxial dual-rotor system according to an embodiment of the present invention. This heterogeneous coaxial dual-rotor system can be fitted to aircraft such as helicopters and drones, and is specifically applicable to helicopters with small rotor disk loads, achieving high aerodynamic efficiency, low aerodynamic noise, and effectively avoiding resonance between the fuselage and the upper and lower rotors.

[0064] like Figure 1 As shown, an embodiment of the present invention provides a heterogeneous coaxial dual-rotor system for mounting to the fuselage of a helicopter, comprising: an upper rotor 1, a lower rotor 2, and a rotor hub 3. This embodiment of the heterogeneous coaxial dual-rotor system can be used in helicopters with small rotor disk loads and rotor radii not exceeding 8.0 m, and more preferably in helicopters with rotor radii not exceeding 4.0 m. The upper rotor 1 is located directly above the lower rotor 2, and the upper rotor 1 and lower rotor 2 are connected via the rotor hub 3, which is connected to the fuselage. The upper rotor 1 and lower rotor 2 are rotatably connected to the fuselage via the rotor hub 3. Optionally, an inner sleeve and an outer sleeve can be arranged inside the rotor hub 3, respectively connected to the upper rotor 1 and lower rotor 2, to achieve opposite rotation of the upper and lower rotors; the inner sleeve and outer sleeve are respectively connected to the aircraft's power system and control system via a transmission mechanism including a gear system to achieve speed and collective pitch adjustment. Optionally, the connection between the upper and lower rotors and the helicopter's power system and control system can adopt existing conventional methods. The upper rotor 1 and the lower rotor 2 have different radii, but their rotation axes are located on the same axis, and their rotation directions can be either the same or opposite.

[0065] Optionally, the dimensional parameters of the upper rotor 1 and the lower rotor 2 in the heterogeneous coaxial dual-rotor system can be set. Specifically, the radius of the upper rotor 1 can be set to... The radius of the lower rotor 2 is The radii of both the upper and lower rotors are no greater than 8.0m, and more specifically, no greater than 4.0m; and / = 0.50 ~ 2.00 and / ≠1.0. Within this range, the overlap area of ​​the upper and lower rotors is reduced, which can weaken aerodynamic interference and reduce vibration and noise; the smaller rotor disk area is not too small and can provide some thrust.

[0066] Furthermore, in this embodiment, the distance between the upper rotor 1 and the lower rotor 2 in the vertical direction (along the rotation axis direction) can also be set as follows: ,and = 0.10~1.00. Among them, satisfying... >0.10 can prevent collision between the upper and lower rotor blades; meets the requirements. Z / A value of <1.00 can prevent the longitudinal dimension of heterogeneous twin rotors from becoming too large and can reduce drag during forward flight.

[0067] Furthermore, in this embodiment, the number of blades of the upper rotor 1 can also be set to... The number of blades of the lower rotor 2 is ; and The value ranges from 2 to 6, meaning a minimum of 2 blades and a maximum of 6 blades. The number of blades on the upper rotor 1 and the lower rotor 2 can be unequal. By setting the upper rotor 1 and the lower rotor 2 to have different numbers of blades (e.g., the rotor with the smaller radius has more blades), the rotor with the smaller radius can provide greater thrust and improve aerodynamic efficiency.

[0068] Furthermore, in this embodiment, the blade twist angles of the upper rotor 1 and the lower rotor 2 can be constant (no twist), linear negative twist (as in formula (1)), ideal twist (as in formula (2)), or other preferred distributions.

[0069] (1)

[0070] (2)

[0071] in, The distribution of blade twist angle, The tip twist angle, r Indicates the spanwise position of the rotor blades. Let be the radius of the rotor. In the above formula, for the upper rotor or the lower rotor, the corresponding parameters can be substituted respectively. For example, when calculating the blade twist angle distribution of the upper rotor, the blade tip twist angle of the upper rotor and the radius of the upper rotor are substituted for calculation; the same applies to the lower rotor.

[0072] Optionally, the blade twist angle distribution of the upper rotor 1 can be set as follows: The blade twist angle distribution of the lower rotor 2 is as follows: The same, among which, Indicates the spanwise position of the rotor blades. This indicates the spanwise position of the rotor blades. For example, there is no twist, the linear negative twist of formula (1), or the ideal twist of formula (2).

[0073] Additionally, the blade twist angle distribution of upper rotor 1 can be set as follows: The blade twist angle distribution of the lower rotor 2 is as follows: The differences are, for example, one of the upper rotor and the lower rotor has blades without twist, while the other has blades with linear twist or ideal twist; and for example, the blade twist angle distribution of upper rotor 1. For the linear torsion of formula (1), the blade torsion angle distribution of the lower rotor 2 The ideal torsion is that of formula (2), and the root torsion angle of the lower rotor 2 is greater than that of the upper rotor 1. This arrangement can improve the induced velocity distribution of the upper and lower rotors, which is beneficial to improving aerodynamic performance.

[0074] In this embodiment, the blades of the upper rotor 1 and the lower rotor 2 may also be configured to adopt a chord length distribution. The chord length may be a constant value, a linear distribution (such as formula (3)), an inverse proportional distribution (such as formula (4)), or other preferred distributions.

[0075] (3)

[0076] (4)

[0077] in, This represents the chord length distribution of the blades. For the chord length of the paddle tip, The root-to-tip ratio is given. In the above formula, for the upper rotor or the lower rotor, the corresponding parameters can be substituted respectively. For example, when calculating the chord length distribution of the upper rotor, the blade tip chord length, root-to-tip ratio, and radius of the upper rotor can be substituted for calculation; the same applies to the lower rotor.

[0078] The blade chord length distribution of upper rotor 1 is expressed as follows: The blade chord length distribution of the lower rotor 2 is represented as follows: Optionally, the chord length distribution of the blades of the upper rotor 1 can be set. chord length distribution of the blades of the lower rotor 2 The chord length distribution of the blades of the upper and / or lower rotor can be set to be the same, for example, both being constant values, both being linearly distributed, or both being inversely proportional. Optionally, the chord length distribution of the blades of the upper and / or lower rotor can also be set to a distribution that varies along the span, for example, the blades in... The chord lengths in the range of 0.85 are constant, linearly distributed, or inversely proportional. The portion within the range of >0.85 has a sharp point.

[0079] Alternatively, the chord length distribution of the blades of the upper rotor 1 can be set. chord length distribution of the blades of the lower rotor 2 The methods differ; for example, the blade chord length distribution of one of the upper and lower rotors is constant, while the blade distribution of the other is linear or inversely proportional. And, for example, the chord length distribution of the blades of upper rotor 1... The chord length distribution of the blades of the lower rotor 2 is a linear distribution according to formula (3). The distribution is the inverse proportional distribution of formula (4). This arrangement can improve the induced velocity distribution of the upper and lower rotors, which is beneficial to improving aerodynamic performance.

[0080] During operation, the upper rotor 1 and the lower rotor 2 face different airflow environments. The lower rotor is subjected to a stronger downwash effect from the upper rotor. The upper and lower rotors adopt different twist angle distributions and / or different blade chord length distributions to achieve higher aerodynamic efficiency.

[0081] In this embodiment, the airfoils of the upper rotor 1 and the lower rotor 2 can be set to be the same, for example, both being the NACA0012 symmetrical airfoil. Alternatively, the airfoils of the upper rotor 1 and the lower rotor 2 can be set to be different. For example, the airfoil of the upper rotor 1 can be set to OA207, and the airfoil of the lower rotor 2 can be set to OA212, making the airfoil of the lower rotor 2 thicker, which is conducive to generating greater thrust, thereby reducing the adverse effect of the strong downwash of the upper rotor 1 on the thrust of the lower rotor 2. Alternatively, the airfoils of the upper rotor 1 and the lower rotor 2 can be preset to be the same NACA4412 airfoil, and then airfoil optimization design can be carried out based on numerical simulation or theoretical calculation.

[0082] In this embodiment, the rotational speed of the upper rotor 1 can also be set to... The rotational speed of the lower rotor 2 is ; and The value can be different. This can be achieved by setting... and This ensures that the Mach number at the tips of the upper and lower rotor blades is below 0.8, in order to avoid transonic flow in the blade tip region, which would affect rotor performance.

[0083] In this embodiment, the collective pitch of the upper rotor 1 can also be set to... The collective pitch of the lower rotor 2 is The two can be the same or different. The collective pitch of the rotor refers to the average pitch angle of the blades on the rotor, which is used to control the overall thrust generated by the rotor.

[0084] Example 1

[0085] The following example, using an embodiment 1 of a coaxial dual-rotor system of different sizes provided according to an embodiment of the present invention, illustrates the role of the coaxial dual-rotor system of different sizes in vibration reduction and noise reduction of coaxial dual-rotor helicopters.

[0086] In Example 1, the heterogeneous coaxial dual-rotor system includes: an upper rotor 1, a lower rotor 2, and a rotor hub 3 connecting the upper and lower rotors to the helicopter fuselage; wherein the radius of the upper rotor is set to be... = 2m, lower rotor radius = 1.5m, / =0.75; the vertical distance between the upper rotor 1 and the lower rotor 2 (along the axis of rotation), i.e., the rotor spacing. It is 0.3m. / = 0.15; Number of blades = = 2; Neither the upper nor lower rotors twisted, that is = = 0; Both the upper and lower rotor blades are rectangular, and the chord length of the upper rotor is 0. and the chord length of the lower rotor equal, = = 0.2m; both the upper and lower rotor blades use the NACA0012 airfoil. Regarding rotor operating conditions, the upper rotor speed is set to... = 720rpm, lower rotor speed = 960 rpm, the Mach number at the tips of both upper and lower rotors is 0.444; the collective pitch of the upper and lower rotors is set to = In this symbol, the subscript L indicates the parameters of the lower rotor, and the subscript U indicates the parameters of the upper rotor.

[0087] In contrast, existing technologies include dual-rotor structures with identical upper and lower rotors, having upper and lower rotors of exactly the same size and shape, and with the same radius: = = 2m, the rotor spacing, number of blades, torsion, planform shape, and airfoil are all the same as the heterogeneous coaxial dual-rotor system of Example 1; the rotational speed of the upper and lower rotors = = 720rpm, collective pitch of upper and lower rotors set to = .

[0088] Figure 2 The diagram shows the size heterogeneous coaxial dual rotor system of Embodiment 1, and compares its thrust-power coefficient curves with those of an existing coaxial dual rotor system with the same upper and lower rotors.

[0089] The tensile force coefficient and power coefficient are respectively:

[0090] (5)

[0091]

[0092] In the above formula, air density, For the thrust of the upper rotor, For the thrust of the lower rotor, The power of the upper rotor, This refers to the power of the lower rotor. This is the rotational speed of the upper rotor. Where is the radius of the upper rotor. The tensile coefficient, This is the power factor. Power, thrust, and rotational speed can be obtained through flight tests, wind tunnel tests, or numerical simulations.

[0093] like Figure 2 As shown, when the tensile coefficient <4.722×10 -3 At the same thrust, the power consumed by the heterogeneous coaxial dual-rotor system of Example 1 is less than that of the existing coaxial dual-rotor system with identical upper and lower rotors. This indicates that the heterogeneous coaxial dual-rotor system proposed in this invention can improve aerodynamic efficiency for helicopters with relatively small rotor disk loads.

[0094] Figure 3 The hovering efficiency-pull coefficient curves of the heterogeneous coaxial dual-rotor system of Embodiment 1 are shown and compared with those of an existing coaxial dual-rotor system with the same upper and lower rotors.

[0095] The hovering efficiency is:

[0096] (6)

[0097] in, For hovering efficiency.

[0098] like Figure 3 As shown, when the tensile coefficient <4.722×10 -3 At that time, the hovering efficiency of the heterogeneous coaxial dual-rotor system of Example 1 was higher than that of existing coaxial dual-rotor systems with the same upper and lower rotors. This indicates that the heterogeneous coaxial dual-rotor system proposed in this invention can improve aerodynamic efficiency for helicopters with relatively small rotor disk loads.

[0099] Figure 4 The unsteady variation curves of the thrust coefficient and torque coefficient of the heterogeneous coaxial dual rotor system of Example 1 are shown. Figure 5 The unsteady variation curves of the thrust coefficient and torque coefficient of an existing coaxial twin-rotor system with identical upper and lower rotors are shown.

[0100] The collective pitch of both the upper and lower rotors is set to 8°, and the horizontal axis represents the azimuth angle of the lower rotor. The unit is degrees (deg); the thrust and torque coefficients of both the upper and lower rotors are dimensionless, using the disk radius and tip velocity of the upper rotor.

[0101] (7)

[0102]

[0103]

[0104]

[0105]

[0106] in, The thrust coefficient of the upper rotor. This is the thrust coefficient of the lower rotor. This represents the torque coefficient of the upper rotor. This represents the torque coefficient of the lower rotor. This is the total torque coefficient. The torque of the upper rotor. Let be the torque of the lower rotor. The thrust of the upper rotor, the thrust of the lower rotor, the rotational speed of the lower rotor, and the rotational speed of the upper rotor vary with time, i.e., with the azimuth angle through which the lower rotor rotates.

[0107] like Figure 4 and Figure 5 As shown, due to the periodic alternation and divergence of the blades of the upper rotor and the lower rotor, the thrust and torque of both coaxial dual rotors exhibit obvious periodicity.

[0108] Figure 4 In the context of Example 1 / In a coaxial dual-rotor system with a size difference of 0.75, the lower rotor blade intersects with the upper rotor blade once every 180° / (1+0.75) = 102.86° azimuth angle. Therefore, the thrust and torque change in a period of 102.86°. There are a total of 7 cycles when the lower rotor rotates through an azimuth angle of 720°.

[0109] Figure 5 In the case of a dual rotor with the same upper and lower rotor, the lower rotor blades intersect with the upper rotor blades once every 90° rotation. Therefore, the thrust and torque change with a period of 90°. There are a total of 8 cycles when the lower rotor rotates through an azimuth angle of 720°.

[0110] contrast Figure 4 and Figure 5 In Example 1, the thrust fluctuations of the upper and lower rotors of the heterogeneous coaxial dual-rotor system are reduced by 37.9% and 35.9%, respectively, compared to existing coaxial dual-rotor systems with the same upper and lower rotors; the total thrust fluctuation is reduced by 50.6%. Therefore, the heterogeneous coaxial dual-rotor system of Example 1 significantly reduces the blade thrust fluctuations of the coaxial dual-rotor, and can significantly reduce pulsating loads and vibration levels.

[0111] Figure 6The size heterogeneous coaxial dual-rotor system of Example 1 was compared with that of an existing coaxial dual-rotor system with the same upper and lower rotors. In the upper rotor's rotation plane, at a distance of 5 from the rotation center... Noise directivity at location.

[0112] like Figure 6 As shown, the aerodynamic noise of an existing coaxial dual-rotor system with identical upper and lower rotors changes periodically with direction in the plane of rotation, at azimuth angles of 0°, 90°, 180°, and 270°. The noise level is highest at 45°, 135°, 225°, and 315° azimuth angles, with a sound pressure level (SPL) of approximately 90.57 dB. The noise is lowest at these angles, with SPLs of approximately 84.51 dB. The aerodynamic noise of the heterogeneous coaxial dual-rotor system in Example 1 is almost uniformly distributed within the plane of rotation, with an SPL of approximately 87.85 dB. This indicates that in the heterogeneous coaxial dual-rotor system of Example 1, the heterogeneous design of the upper and lower rotors homogenizes the noise energy along the azimuth angle, significantly reducing the noise peak.

[0113] like Figure 7 As shown, another embodiment 2 of a heterogeneous coaxial dual-rotor system according to an embodiment of the present invention includes: an upper rotor 1, a lower rotor 2, and a rotor hub 3 connecting the upper rotor 1 and the lower rotor 2 to the helicopter fuselage.

[0114] In Example 2, the upper rotor radius is = 0.4m, lower rotor radius = 0.28m, / =0.7; the vertical distance between the upper rotor 1 and the lower rotor 2 (along the axis of rotation), i.e., the rotor spacing. It is 0.12 m. = 0.30; Number of blades = 2、 = 3. The upper rotor blades have a 15° linear negative twist, while the lower rotor has no twist. The upper rotor has blades with a linear chord length distribution, a tip chord length of 0.04m, and a root-to-tip ratio of 2; the lower rotor uses rectangular blades. The chord length in the range of 0.85 is = 0.04m, the blade is at The portion exceeding 0.85 has a certain degree of taper. Among them, This indicates the spanwise position of the lower rotor blade, that is, the distance in the spanwise direction between a point on the blade and the blade root; the taper refers to the gradual decrease in blade chord length from the blade root to the blade tip. Both the upper and lower rotor blades use NACA four-position symmetrical airfoils, with blade thickness varying linearly from the blade root to the blade tip. Regarding rotor operating conditions, the collective pitch of the upper and lower rotors... = =12°, the upper and lower rotor speeds are determined based on the system thrust level and torque balance. Considering the power of the power system and the Mach number limit of the rotor tip, the upper and lower rotor speeds do not exceed 1500 rpm.

[0115] The heterogeneous coaxial dual-rotor system provided in Example 2 can reduce aerodynamic interference between the upper and lower rotors and improve the aerodynamic efficiency of the coaxial dual-rotor system.

[0116] All of the above-mentioned optional technical solutions can be combined in any way to form optional embodiments of the present invention, and will not be described in detail here.

[0117] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0118] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A coaxial dual-rotor system with heterogeneous size, characterized in that, For mounting to a helicopter fuselage, including: a coaxially arranged upper rotor and a lower rotor below, and a rotor hub connecting the upper rotor and the lower rotor to the fuselage; the rotor hub has an inner sleeve and an outer sleeve that are respectively connected to the upper rotor and the lower rotor to achieve opposite rotation of the upper rotor and the lower rotor; the inner sleeve and the outer sleeve are respectively connected to the aircraft's power system and control system via a transmission mechanism to achieve speed and collective pitch adjustment; The upper rotor and the lower rotor have different radii; The radii of the upper and lower rotors are no greater than 8.0m; The number of blades on the upper rotor and the lower rotor ranges from 2 to 6. The ratio of the distance between the upper and lower rotors in the vertical direction of the rotation axis to the radius of the upper rotor is in the range of 0.1 to 1.00; The upper and lower rotors have different numbers of blades, with the rotor having a smaller radius having more blades; The blade twist angle distribution of the upper rotor is as follows: in, The blade twist angle distribution of the upper rotor. The blade tip twist angle of the upper rotor. Indicates the spanwise position of the rotor blades. The radius of the upper rotor; The blade twist angle distribution of the lower rotor is as follows: in, The blade twist angle distribution of the lower rotor. This refers to the tip twist angle of the lower rotor blade. This indicates the spanwise position of the lower rotor blades. The radius of the lower rotor; The blade chord distribution of the upper rotor is as follows: in, The blade chord distribution of the upper rotor. The tip chord of the rotor blades is the length of the rotor blades. The blade root-to-tip ratio of the upper rotor. Indicates the spanwise position of the rotor blades. The radius of the upper rotor; The blade chord distribution of the lower rotor is as follows: in, The blade chord distribution of the lower rotor. The tip chord of the rotor blade is the length of the lower rotor blade. This indicates the spanwise position of the lower rotor blades. Where is the radius of the lower rotor.

2. The heterogeneous coaxial dual-rotor system according to claim 1, characterized in that, The ratio of the lower rotor radius to the upper rotor radius is in the range of 0.5 to 2.

00.

3. The heterogeneous coaxial dual-rotor system according to claim 1, characterized in that, The upper rotor has two blades, and the lower rotor has three blades; The upper rotor has a radius of 0.4m, the lower rotor has a radius of 0.28m, and the ratio of the lower rotor radius to the upper rotor radius is 0.

7. The vertical distance between the upper and lower rotors along the axis of rotation is 0.12 m; The ratio of the distance between the upper and lower rotors in the vertical direction of the rotation axis to the radius of the upper rotor is 0.

3.

4. The heterogeneous coaxial dual-rotor system according to claim 3, characterized in that, The root-to-tip ratio of the upper rotor blade is 2, and the blade tip chord length is 0.04m; The lower rotor blades in The chord length in the 0.85 range is 0.04m. The portion exceeding 0.85 has a sharp point; among which, This indicates the spanwise position of the lower rotor blades. This indicates the radius of the lower rotor.

5. The heterogeneous coaxial dual-rotor system according to claim 4, characterized in that, The blades of the upper rotor have a 15° linear negative twist, while the blades of the lower rotor have no twist.

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