Coaxial double-rotor system with different sizes

Abstract

The invention relates to a large and small heterogeneous coaxial dual-rotor system, belongs to the technical field of aviation aircraft design, and solves the problems that in the prior art, upper and lower rotor vibration inherent frequencies of coaxial dual rotors are close, vibration loads are amplified through resonance, and helicopter fuselage vibration and ground resonance are caused. The propeller hub is used for connecting the upper rotor wing and the lower rotor wing with the fuselage; an inner sleeve and an outer sleeve are arranged in the propeller hub and connected with the upper rotor wing and the lower rotor wing correspondingly, and opposite rotation of the upper rotor wing and the lower rotor wing is achieved. The inner sleeve and the outer sleeve are respectively connected with a power system and a control system of the aircraft through a transmission mechanism to realize rotation speed and total distance adjustment; wherein the upper rotor wing and the lower rotor wing have different radiuses; the number of the blades of the upper rotor wing and the number of the blades of the lower rotor wing range from 2 to 6; the ratio of the distance between the upper rotor wing and the lower rotor wing in the vertical direction of the rotation axis to the radius of the upper rotor wing ranges from 0.1 to 1.00.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of aircraft design, and particularly relates to a large-small heterogeneous coaxial dual-rotor system. BACKGROUND

[0002] Coaxial dual-rotor is composed of two pairs of rotors installed on the same axis, and the two pairs of rotors bear the roles of lift surface, thrust surface and control surface. Compared with the conventional helicopter with single rotor and tail rotor, the coaxial dual-rotor helicopter has many advantages: first, the load potential is greater. The coaxial dual-rotor produces pulling force through two pairs of rotors, and can have higher lift redundancy under the condition of limiting the size of the helicopter. Second, the structure is more compact. When the two pairs of rotors are turned in opposite directions, torque balance can be achieved by adjusting the pitch or speed, so that the coaxial dual-rotor helicopter does not need a tail rotor, and therefore the fuselage structure can be shortened within the range of the rotor disc, reducing the pitch and yaw moment of inertia of the helicopter, improving the control efficiency and maneuverability, and also improving the wind resistance characteristics. Third, the utilization rate of power is higher. The tail rotor design avoids the power consumption of the tail rotor, and the engine power can be more used to generate pulling force, improving the hovering efficiency. The hovering power of a typical coaxial dual-rotor helicopter is only about 80% of that of a conventional helicopter. Therefore, under complex terrain conditions such as cities and mountains, the coaxial dual-rotor helicopter is more suitable for low-altitude operations such as air traffic, logistics distribution, emergency rescue than the conventional helicopter, and has broad application prospects.

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

[0004] The upper and lower rotors of the coaxial dual-rotor interfere with each other, which will bring serious vibration and noise problems. On the one hand, the periodic staggering and moving away of the blades produce periodic pulsating loads, making the vibration loads transmitted to the rotor hub larger than those of a single rotor. Since the upper and lower rotors of the existing coaxial dual-rotor are of the same size, their natural frequencies are close, and the superposition of their amplitudes can also 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 task capability and threatening flight safety. On the other hand, the periodic staggering of the rotor blades also causes the surface pressure of the blades to pulsate, producing aerodynamic noise. In addition, the slipstream of the upper rotor contracts when it develops to the lower rotor disc plane, causing the upper rotor tip vortex to collide with the lower rotor blade, producing blade-vortex interference; the upper and lower rotor tip vortices further entangle, fuse and distort downstream, producing vortex-vortex interference. The blade-vortex interference and vortex-vortex interference of the dual-rotor become additional noise sources, making the coaxial dual-rotor helicopter face more prominent noise problems than the conventional single-rotor helicopter.

[0005] Chinese invention patent application, publication number CN109878713A, invention name "micro coaxial dual-rotor unmanned aerial vehicle", discloses a micro coaxial dual-rotor unmanned aerial vehicle, including coaxial upper rotor, lower rotor and dual-rotor support, wherein the upper rotor and the lower rotor are the same size, and both have two blades. The upper and lower rotors of the coaxial dual-rotor unmanned aerial vehicle are the same size, the natural frequency of vibration is close, the amplitude superposition will cause resonance, further amplifies the vibration load, reduces the flight efficiency.

[0006] Chinese utility model patent, publication number CN204507261U, name "coaxial same direction multi-rotor helicopter", discloses a coaxial dual-rotor helicopter, including aircraft body and main rotor, the main rotor includes rotor one and rotor two, wherein the rotor one and the rotor two are the same size, and both have two blades. Therefore, the coaxial dual-rotor helicopter still has the problem that the natural frequency of vibration of the rotor one and the rotor two is close, and the amplitude superposition will cause resonance.

[0007] Therefore, there is a need for a coaxial dual-rotor system capable of reducing vibration and noise and high aerodynamic efficiency in the field. SUMMARY

[0008] The present application is directed to the prominent vibration and noise problems faced by the existing coaxial dual-rotor, and proposes a size heterogeneous coaxial dual-rotor system. The upper and lower rotors of the system have different radii, which is beneficial to reduce the fluctuation of blade surface pressure and tension, thereby realizing vibration reduction and noise reduction.

[0009] According to the embodiment of the present application, a size heterogeneous coaxial dual-rotor system is provided for mounting to the fuselage of a helicopter, comprising: coaxially arranged upper rotor and lower rotor below, and hub connecting the upper rotor and the lower rotor with the fuselage; inner sleeve and outer sleeve arranged inside the hub are respectively connected with the upper rotor and the lower rotor to realize opposite rotation directions of the upper rotor and the lower rotor; the inner sleeve and the outer sleeve are respectively connected with the power system and the control system of the aircraft via a transmission mechanism to realize speed and total distance adjustment. Wherein, the upper rotor and the lower rotor have different radii; The radii of the upper rotor and the lower rotor are not greater than 8.0m; The number of blades of the upper rotor and the number of blades of the lower rotor are in the range of 2 to 6; The ratio of the vertical distance of the upper rotor and the lower rotor to the radius of the upper rotor is in the range of 0.1 to 1.00.

[0010] Optionally, the ratio of the radius of the lower rotor to the upper rotor is in the range of 0.5 to 2.00; the number of blades of the upper rotor and the number of blades of the lower rotor are different.

[0011] Optionally, the twist angle of the blades of the upper rotor is different from the twist angle of the blades of the lower rotor.

[0012] Optionally, the twist angle distribution of the blades of the upper rotor is:

[0013] wherein, is the twist angle distribution of the blades of the upper rotor, is the tip twist angle of the blades of the upper rotor, denotes the spanwise position of the blades of the upper rotor, is the radius of the upper rotor; the twist angle distribution of the blades of the lower rotor is:

[0014] wherein, is the twist angle distribution of the blades of the lower rotor, is the tip twist angle of the blades of the lower rotor, denotes the spanwise position of the blades of the lower rotor, is the radius of the lower rotor.

[0015] Optionally, the chord length distribution of the blades of the upper rotor is different from the chord length distribution of the blades of the lower rotor.

[0016] Optionally, the chord length distribution of the blades of the upper rotor is:

[0017] wherein, is the chord length distribution of the blades of the upper rotor, is the tip chord length of the blades of the upper rotor, is the tip chord ratio of the blades of the upper rotor, denotes the spanwise position of the blades of the upper rotor, is the radius of the upper rotor; the chord length distribution of the blades of the lower rotor is:

[0018] wherein, is the chord length distribution of the blades of the lower rotor, is the tip chord length of the blades of the lower rotor, denotes the spanwise position of the blades of the lower rotor, is the radius of the lower rotor.

[0019] Optionally, the upper rotor has two blades and the lower rotor has three blades; the upper rotor has a radius of 0.4 m and the lower rotor has a radius of 0.28 m, the ratio of the radius of the lower rotor to the radius of the upper rotor being 0.7; the distance between the upper rotor and the lower rotor in the vertical direction of the axis of rotation is 0.12 m; The ratio of the vertical distance between the upper rotor and the lower rotor along the rotation axis to the radius of the upper rotor is 0.3.

[0020] Optionally, the upper rotor has linear chord distribution of the blades, the root tip ratio is 2, and the tip chord length of the blades is 0.04 m. The lower rotor has rectangular blades, the chord length of the blades in the range of 0 to 0.85 is 0.04 m, and the chord length of the blades in the range of 0.85 to 1.0 is 0.06 m. The chord length of the blades in the range of 0 to 0.85 is 0.04 m, and the chord length of the blades in the range of 0.85 to 1.0 is 0.06 m. The part in the range of 0.85 to 1.0 is tapered; wherein, The blade spanwise position of the lower rotor is represented by x, The radius of the lower rotor is represented by R.

[0021] Optionally, the blades of the upper rotor have 15° linear negative twist, and the blades of the lower rotor have no twist.

[0022] Optionally, the number of blades of the upper rotor and the number of blades of the lower rotor are the same, both being two blades. The radius of the upper rotor is 2 m, the radius of the lower rotor is 1.5 m, and the ratio of the radius of the lower rotor to the radius of the upper rotor is 0.75. The vertical distance between the upper rotor and the lower rotor along the rotation axis is 0.3 m. The blades of the upper rotor and the blades of the lower rotor have no twist. The blades of the upper rotor and the blades of the lower rotor are rectangular. The chord lengths of the blades of the upper rotor and the lower rotor are equal, being 0.2 m.

[0023] Compared with the prior art, the size-heterogeneous coaxial dual-rotor system provided by the application has at least the following beneficial effects.

[0024] (1) The size-heterogeneous coaxial dual-rotor system of the application limits the ratio of the vertical distance between the upper rotor and the lower rotor along the rotation axis to the radius of the upper rotor to the range of 0.1 to 1.00, which not only avoids the collision of the upper and lower rotor blades, but also avoids the excessive size of the heterogeneous dual-rotor system in the vertical direction, thereby reducing the flight resistance.

[0025] (2) Compared with the prior art coaxial dual-rotor system with equal radii of the upper and lower rotors, the size-heterogeneous coaxial dual-rotor system of the application reduces the rotor disc overlap area, reduces the unsteady fluctuation of the rotor drag, and is beneficial to reducing the pulse load and the vibration level. Further, when used in a small rotor disc load helicopter, such as a helicopter with a rotor radius less than 8.0 m, the size-heterogeneous coaxial dual-rotor system can significantly improve the aerodynamic efficiency, reduce the aerodynamic noise, and effectively avoid the resonance of the fuselage and the upper and lower rotors.

[0026] (3) The size heterogeneous coaxial dual-rotor system of the present application can weaken the aerodynamic interference between the upper and lower rotors, and is beneficial to improve the aerodynamic performance of the rotors, compared with the existing coaxial dual-rotor system with equal radius of the upper and lower rotors.

[0027] (4) The size heterogeneous coaxial dual-rotor system of the present application can weaken the aerodynamic interference between the upper and lower rotors, and can reduce the blade surface pressure pulsation, and under certain conditions, can weaken the blade-vortex interference and vortex-vortex interference, and is beneficial to reduce the aerodynamic noise, compared with the existing coaxial dual-rotor system with equal radius of the upper and lower rotors.

[0028] (5) The size heterogeneous coaxial dual-rotor system of the present application can reduce the vibration energy superposition and effectively avoid resonance, compared with the existing coaxial dual-rotor system with equal radius of the upper and lower rotors, because the upper and lower rotors have different shapes and different natural frequencies.

[0029] (6) The size heterogeneous coaxial dual-rotor system of the present application can expand the optimization space and performance boundary, compared with the existing coaxial dual-rotor system with equal radius of the upper and lower rotors, because the radius, number of blades, twist angle, planar shape, airfoil and other parameters of the upper and lower rotors can be set differently. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments will be briefly introduced as follows, and the features and advantages of the present application can be more clearly understood by referring to the drawings. The drawings are schematic and should not be understood as any limitation on the present application. For those skilled in the art, other drawings can be obtained without creative labor on the basis of these drawings.

[0031] Figure 1 FIG. 1 is a schematic diagram of embodiment 1 of a size heterogeneous coaxial dual-rotor system according to the embodiments of the present application.

[0032] Figure 2 FIG. 2 is a comparison diagram of the lift coefficient-power coefficient curve of embodiment 1 of the size heterogeneous coaxial dual-rotor system according to the embodiments of the present application and the existing coaxial dual-rotor system with the same upper and lower rotors.

[0033] Figure 3 FIG. 3 is a comparison diagram of the hovering efficiency-lift coefficient curve of embodiment 1 of the size heterogeneous coaxial dual-rotor system and the existing coaxial dual-rotor system with the same upper and lower rotors.

[0034] Figure 4 FIG. 4 is a lift coefficient unsteady variation curve diagram of embodiment 1 of the size heterogeneous coaxial dual-rotor system.

[0035] Figure 5 FIG. 5 is a lift coefficient unsteady variation curve diagram of the existing coaxial dual-rotor system with the same upper and lower rotors.

[0036] Figure 6 A noise level directivity comparison chart of the size heterogeneous coaxial dual-rotor system of Example 1 and the existing coaxial dual-rotor system with the same upper rotor and lower rotor.

[0037] Figure 7 A schematic diagram of Example 2 of the size heterogeneous coaxial dual-rotor system according to the embodiment of the present application.

[0038] Reference Signs: 1 - upper rotor; 2 - lower rotor; 3 - hub. DETAILED DESCRIPTION

[0039] In order to enable a more clear understanding of the above-mentioned objects, features and advantages of the present application, the present application will be further described below with reference to the drawings and specific embodiments. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0040] In the following description, a lot of specific details are set forth in order to facilitate a thorough understanding of the present application, but the present application can also be implemented in other ways different from those described herein, and therefore, the scope of protection of the present application is not limited by the specific embodiments disclosed below.

[0041] A size heterogeneous coaxial dual-rotor system according to the embodiment of the present application is described in detail below with reference to the drawings. The size heterogeneous coaxial dual-rotor system according to the embodiment of the present application can be assembled to an aircraft such as a helicopter, a drone, etc., and in particular, can be used in a helicopter with a small rotor disc load, achieving the effects of high aerodynamic efficiency, low aerodynamic noise, and effectively avoiding the resonance of the fuselage and the upper and lower rotors.

[0042] As Figure 1As shown, according to an embodiment of the present application, a size-heterogeneous coaxial dual-rotor system for mounting to a fuselage of a helicopter is provided, which includes an upper rotor 1, a lower rotor 2, and a hub 3. The size-heterogeneous coaxial dual-rotor system can be used for a helicopter with a small rotor disc load and a rotor radius of no more than 8.0 m, and more preferably for a helicopter with a rotor radius of no more than 4.0 m. The upper rotor 1 is located directly above the lower rotor 2, and the upper rotor 1 and the lower rotor 2 are connected by the hub 3, which is connected to the fuselage. The upper rotor 1 and the lower rotor 2 are rotatably connected to the fuselage by the hub 3. Optionally, an inner sleeve and an outer sleeve can be arranged inside the hub 3 to connect the upper rotor 1 and the lower rotor 2, respectively, to achieve opposite rotation directions of the upper rotor 1 and the lower rotor 2. The inner sleeve and the outer sleeve are connected to the power system and the control system of the aircraft via a transmission mechanism inside a gear system to achieve adjustment of the rotation speed and the total pitch. Optionally, the connection of the upper rotor 1 and the lower rotor 2 to the power system and the control system of the helicopter can be achieved in a conventional manner. The upper rotor 1 and the lower rotor 2 have different radii and rotate around the same axis, and the rotation directions can be the same or opposite.

[0043] Optionally, the size parameters of the upper rotor 1 and the lower rotor 2 in the size-heterogeneous coaxial dual-rotor system can be set. Specifically, the radius of the upper rotor 1 can be set to , and the radius of the lower rotor 2 can be set to , wherein the radii of the upper rotor 1 and the lower rotor 2 are both no more than 8.0 m, and more preferably both no more than 4.0 m; and / = 0.50 ~ 2.00 and / ≠ 1.0. Within this range, the overlapping area of the upper rotor 1 and the lower rotor 2 is reduced, which can reduce the aerodynamic interference, vibration, and noise; and the smaller rotor disc area is not too small, which can provide partial pulling force.

[0044] Further, in this embodiment, the distance between the upper rotor 1 and the lower rotor 2 in the vertical direction (along the rotation axis) can be set to , and = 0.10 ~ 1.00. Wherein, satisfying > 0.10 can avoid collision between the blades of the upper rotor 1 and the lower rotor 2; and satisfying Z / < 1.00 can avoid excessive longitudinal size of the size-heterogeneous coaxial dual-rotor system and reduce the resistance during forward flight.

[0045] Further, in this embodiment, the number of blades of the upper rotor 1 can be set to , and the number of blades of the lower rotor 2 can be set to ; and The value range is 2-6, that is, at least 2 blades and at most 6 blades. The number of blades of the upper rotor 1 and the number of blades of the lower rotor 2 can be unequal. By setting the upper rotor 1 and the lower rotor 2 to have different numbers of blades (for example, the rotor with a smaller radius has more blades), the rotor with a smaller radius can provide greater pulling force, and the aerodynamic efficiency can be improved.

[0046] Further, in this embodiment, the blade twist angle of the upper rotor 1 and the lower rotor 2 can be a constant (no twist), linear negative twist (such as formula (1)), ideal twist (such as formula (2)), or other preferred distribution.

[0047] (1) (2) wherein, is the blade twist angle distribution, is the tip twist angle, r represents the spanwise position of the rotor blade, is the radius of the rotor. In the above formula, for the upper rotor or the lower rotor, the corresponding parameters can be substituted, for example, when calculating the blade twist angle distribution of the upper rotor, the tip twist angle of the blade of the upper rotor and the radius of the upper rotor are substituted for calculation; the same applies to the lower rotor.

[0048] Optionally, the blade twist angle distribution of the upper rotor 1 can be set as , and the blade twist angle distribution of the lower rotor 2 is , wherein, represents the spanwise position of the blade of the upper rotor, represents the spanwise position of the blade of the lower rotor. For example, both are no twist, both are linear negative twist of formula (1), or both are ideal twist of formula (2).

[0049] In addition, the blade twist angle distribution of the upper rotor 1 can be set as , and the blade twist angle distribution of the lower rotor 2 is different, for example, one of the upper rotor and the lower rotor is no twist of the blade, and the other is linear twist or ideal twist of the blade; and for example, the blade twist angle distribution of the upper rotor 1 is linear twist of formula (1), and the blade twist angle distribution of the lower rotor 2 is ideal twist of formula (2), and the blade root twist 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, and is beneficial to improve the aerodynamic performance.

[0050] In this embodiment, the chord distribution of the blades of the upper rotor 1 and the lower rotor 2 can also be set to be constant, linear distribution (such as formula (3)), inverse proportion distribution (such as formula (4)), or other optimized distribution.

[0051] (3) (4) wherein, is the chord distribution of the blades, is the tip chord length, is the root tip ratio. 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 distribution of the upper rotor, the tip chord length of the blades of the upper rotor, the root tip ratio and the radius of the upper rotor are substituted for calculation; the same applies to the lower rotor.

[0052] The chord distribution of the blades of the upper rotor 1 is represented as , and the chord distribution of the blades of the lower rotor 2 is represented as . Alternatively, the chord distribution of the blades of the upper rotor 1 may be set to be the same as the chord distribution of the blades of the lower rotor 2 , for example, both are constant, both are linear distribution, or both are inverse proportion distribution. Alternatively, the chord distribution of the blades of the upper rotor and / or the lower rotor can also be set to have a variable distribution in the spanwise direction, for example, the chord length of the blades in the range of 0.85 is constant, linear distribution or inverse proportion distribution, and the chord length in the range of >0.85 is tapered.

[0053] Alternatively, the chord distribution of the blades of the upper rotor 1 may be set to be different from the chord distribution of the blades of the lower rotor 2 , for example, the chord distribution of the blades of one of the upper rotor and the lower rotor is constant, while the chord distribution of the blades of the other is linear distribution or inverse proportion distribution; and for example, the chord distribution of the blades of the upper rotor 1 is linear distribution of formula (3), and the chord distribution of the blades of the lower rotor 2 is inverse proportion distribution of formula (4), which arrangement can improve the induced velocity distribution of the upper rotor and the lower rotor, and is beneficial to improve the aerodynamic performance.

[0054] In operation, the upper rotor 1 and the lower rotor 2 face different airflow environments, the lower rotor is subjected to stronger downwash effect of the upper rotor, and the upper rotor and the lower rotor adopt different twist angle distributions and / or different chord distributions of the blades, which can achieve higher aerodynamic efficiency.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] Example 1 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.

[0059] 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 are equal, = = 0.2m; the blades of the upper and lower rotors are both selected as NACA0012 airfoils. In terms of rotor working conditions, the upper rotor speed is set as = 720rpm, the lower rotor speed is set as = 960rpm, and the tip Mach number of the upper and lower rotors is 0.444; the total distance of the upper and lower rotors is set as = . Wherein, the subscript L of the symbol represents the parameter of the lower rotor, and the subscript U of the symbol represents the parameter of the upper rotor.

[0060] As a comparison, the prior art includes a dual-rotor structure with the same upper and lower rotors, the upper and lower rotors have the same size and shape, and the radii of the upper and lower rotors are the same: = = 2m, the rotor distance, the number of blades, the twist, the planform, and the airfoil are the same as those of the heterogeneous coaxial dual-rotor system of embodiment 1; the upper and lower rotor speeds are set as = = 720rpm, and the total distance of the upper and lower rotors is set as = .

[0061] Figure 2 The size heterogeneous coaxial dual-rotor system of embodiment 1 is shown, and the comparison of the thrust coefficient-power coefficient curve between the size heterogeneous coaxial dual-rotor system and the prior art coaxial dual-rotor system with the same upper and lower rotors is shown.

[0062] Wherein, the thrust coefficient and the power coefficient are respectively: (5)

[0063] In the above formula, is the air density, is the thrust of the upper rotor, is the thrust of the lower rotor, is the power of the upper rotor, is the power of the lower rotor, is the speed of the upper rotor, is the radius of the upper rotor, is the thrust coefficient, is the power coefficient. The power, the thrust, and the speed can be obtained through flight test, wind tunnel test, or numerical simulation.

[0064] As shown in Figure 2 , when the thrust coefficient <4.722×10 -3At 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.

[0065] 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.

[0066] The hovering efficiency is: (6) in, For hovering efficiency.

[0067] 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.

[0068] 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.

[0069] 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. (7)

[0070]

[0071]

[0072]

[0073] 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. is the torque coefficient of the lower rotor, is the total torque coefficient, is the torque of the upper rotor, is the torque of the lower rotor. Where the tension of the upper rotor, the tension of the lower rotor, the rotation speed of the lower rotor, the rotation speed of the upper rotor change with time, that is, change with the azimuth angle through which the lower rotor rotates.

[0074] As shown in Figure 4 and Figure 5 , due to the periodic staggering and moving away of the blades of the upper rotor and the blades of the lower rotor, the tension and torque of the two coaxial dual-rotor systems have obvious periodicity.

[0075] Figure 4 In the embodiment 1, for the size heterogeneous coaxial dual-rotor system with / = 0.75, the lower rotor blades stagger with the upper rotor blades once every 180° / (1+0.75) = 102.86° of azimuth angle, so the tension and torque change periodically with 102.86°, and there are 7 periods when the lower rotor rotates through an azimuth angle of 720°.

[0076] Figure 5 In the prior art, for the dual-rotor system with the same upper rotor and lower rotor, the lower rotor blades stagger with the upper rotor blades once every 90°, so the tension and torque change periodically with 90°, and there are 8 periods of change when the lower rotor rotates through an azimuth angle of 720°.

[0077] Comparing Figure 4 and Figure 5 , the tension fluctuation of the upper rotor and the lower rotor of the size heterogeneous coaxial dual-rotor system of the embodiment 1 is reduced by 37.9% and 35.9% respectively compared with the prior art coaxial dual-rotor system with the same upper rotor and lower rotor; the total tension fluctuation is reduced by 50.6%. It can be seen that the size heterogeneous coaxial dual-rotor system of the embodiment 1 significantly reduces the blade tension fluctuation of the coaxial dual-rotor system, and can significantly reduce the pulsating load and vibration level.

[0078] Figure 6 The noise directivity at a position 5 from the rotation center in the rotation plane of the upper rotor of the size heterogeneous coaxial dual-rotor system of the embodiment 1 is compared with that of the prior art coaxial dual-rotor system with the same upper rotor and lower rotor.

[0079] As shown in Figure 6 , the aerodynamic noise of the prior art coaxial dual-rotor system with the same upper rotor and lower rotor changes periodically in the rotation plane with the direction at 0°, 90°, 180°, and 270° azimuth angles 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.

[0080] 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.

[0081] 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 system power and rotor tip Mach number limitations, the upper and lower rotor speeds do not exceed 1500 rpm.

[0082] 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.

[0083] All the optional technical solutions above can be combined to form optional embodiments of the present application, and will not be described one by one here.

[0084] It should be understood that the size of the serial number of each step in the above embodiment does not mean the order of execution, and the execution order of each process should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0085] The above is only a preferred specific implementation of the present application, but the protection scope of the present application is not limited to this. Any person skilled in the art can easily think of changes or replacements within the technical scope disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A size-heterotic coaxial dual-rotor system, characterized in that, A fuselage for mounting to a helicopter, comprising: a coaxial upper rotor and a lower rotor arranged below the upper rotor, and a mast connecting the upper and lower rotors to the fuselage; an inner sleeve and an outer sleeve arranged inside the mast and connected to the upper and lower rotors respectively to enable counter-rotation of the upper and lower rotors; the inner sleeve and the outer sleeve being connected to a power system and a control system of the aircraft via transmission mechanisms to enable adjustment of the rotational speed and the total pitch; wherein the upper and lower rotors have different radii; the radii of the upper and lower rotors are not greater than 8.0 m; the number of blades of the upper rotor and the number of blades of the lower rotor are in the range of 2 to 6; the ratio of the vertical distance between the upper and lower rotors along the axis of rotation to the radius of the upper rotor is in the range of 0.1 to 1.

00.

2. The size-heterotic coaxial dual rotor system according to claim 1, wherein: the ratio of the radius of the lower rotor to the radius of the upper rotor is in the range of 0.5 to 2.00; the number of blades of the upper rotor is different from the number of blades of the lower rotor.

3. The size-heterotic coaxial dual rotor system according to claim 1, wherein: the twist angle of the blades of the upper rotor is different from the twist angle of the blades of the lower rotor.

4. The size-heterotic coaxial dual rotor system according to claim 3, wherein: the twist angle of the blades of the upper rotor is distributed as: wherein is a twist angle distribution of the blades of the upper rotor, is a twist angle of the blade tip of the upper rotor, denotes a spanwise position of the blade of the upper rotor, is a radius of the upper rotor; the twist angle of the blades of the lower rotor is distributed as: wherein is a twist angle distribution of the blades of the lower rotor, is a twist angle of the blade tip of the lower rotor, denotes a spanwise position of the blade of the lower rotor, is a radius of the lower rotor.

5. The megamorphic coaxial dual-rotor system, according to claim 1, wherein, the chord length distribution of the blades of the upper rotor is different from the chord length distribution of the blades of the lower rotor.

6. The size-heterotic coaxial dual rotor system according to claim 5, wherein: the chord length distribution of the blades of the upper rotor is: wherein is a chord length distribution of the blades of the upper rotor, is a blade tip chord length of the upper rotor, is a blade root tip ratio of the upper rotor, denotes a spanwise position of the blades of the upper rotor, is a radius of the upper rotor; the chord length distribution of the blades of the lower rotor is: wherein is a chord length distribution of the blades of the lower rotor, is a tip chord length of the blades of the lower rotor, denotes a spanwise position of the blades of the lower rotor, is a radius of the lower rotor.

7. The size-heterotic coaxial dual rotor system according to claim 1, wherein: the upper rotor has two blades and the lower rotor has three blades; the radius of the upper rotor is 0.4 m and the radius of the lower rotor is 0.28 m, and the ratio of the radius of the lower rotor to the radius of the upper rotor 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 vertical distance between the upper and lower rotors along the axis of rotation to the radius of the upper rotor is 0.

3.

8. The size-heterotic coaxial dual rotor system according to claim 7, wherein: the upper rotor has blades with a linear chord length distribution, a root tip ratio of 2, and a blade tip chord length of 0.04 m; The lower rotor has rectangular blades which are inclined in the direction of rotation The chord length of the portion in the range of 0.85 is 0.04 m, at The portion in the range of 0.85 is tapered; wherein, represents a spanwise position of a blade of the lower rotor, represents a radius of the lower rotor.

9. The size-heterotic coaxial dual rotor system according to claim 8, wherein: the blades of the upper rotor have a linear negative twist of 15°, and the blades of the lower rotor have no twist.

10. The size-heterotic coaxial dual rotor system according to claim 1, wherein: the number of blades of the upper rotor is the same as the number of blades of the lower rotor, both being two blades; the radius of the upper rotor is 2 m and the radius of the lower rotor is 1.5 m, and the ratio of the radius of the lower rotor to the radius of the upper rotor is 0.75; the vertical distance between the upper and lower rotors along the axis of rotation is 0.3 m; the blades of the upper and lower rotors have no twist; the blades of the upper and lower rotors are rectangular; the chord lengths of the blades of the upper and lower rotors are equal, being 0.2 m.

Images