A toroidal propeller apparatus and aircraft

Abstract

The application provides a ring propeller device and an aircraft, and relates to the technical field of aircrafts. The ring propeller device comprises a hub, a high-position blade pair and a low-position blade pair. The high-position blade pair and the low-position blade pair are located on opposite sides of a rotating reference plane and form an axial offset distance along the hub axis direction. The high-position blade section and the low-position blade section are connected to the hub through respective root ends and are connected through a tip connection section at outer ends, and together form a ring blade structure with a closed tip. The geometric pitch angle of the low-position blade section at the same radial position is greater than that of the high-position blade section, and the difference between the geometric pitch angles of the two gradually increases from the root end to the outer end. The device can weaken the concentrated tip vortex at the open tip, weaken the wake interference between the high-position blade section and the low-position blade section, and improve the local inflow conditions, thereby being beneficial to the consideration of thrust performance, aerodynamic efficiency and low-noise performance.

Description

Technical Field

[0001] This application relates to the field of aircraft technology, and more specifically, to a ring propeller device and an aircraft. Background Technology

[0002] In recent years, with the development of applications in low-altitude economy, urban air traffic, logistics distribution, and inspection and monitoring, the frequency and density of use of low-altitude unmanned aerial vehicles (UAVs) have been continuously increasing. Multi-rotor UAVs, with their advantages of vertical takeoff and landing, flexible hovering, relatively simple structure, and low operating costs, have become the most widely used flight platform in the low-altitude field. As a key component in generating lift and propulsion for multi-rotor UAVs, the propeller's aerodynamic efficiency, noise level, and operational safety directly affect the UAV's endurance, environmental adaptability, and application range in noise-sensitive areas such as cities.

[0003] Existing low-altitude unmanned aerial vehicles (UAVs) typically employ open-type propellers. While open-type propellers are structurally mature, easy to manufacture, and offer good thrust performance, their blades have freely open tips. High-pressure airflow easily bypasses these tips and flows towards the low-pressure side, forming strong tip vortices near the tips. These tip vortices not only increase induced losses and affect the propeller's effective work capacity but also easily cause periodic pressure pulsations and aerodynamic noise. Furthermore, the high-speed rotating open tips pose certain safety hazards to surrounding personnel, obstacles, and other structures within the aircraft.

[0004] To address the issues of tip vortices, noise, and insufficient stiffness inherent in traditional open-blade propellers, annular propellers have gradually gained attention. Annular propellers, by connecting the outer ends of the blades to form a continuous closed-loop structure, can reduce the strong tip vortices caused by discrete open tips and improve the overall structural stiffness and operational safety of the blades. Therefore, they are considered a feasible direction for improving the noise and efficiency of propellers in low-altitude unmanned aerial vehicles (UAVs). For example, US10836466B2 discloses an annular propeller that improves propeller stiffness and reduces acoustic characteristics by bending the ends of multiple slender blade elements and allowing them to contact each other to form a closed structure. This solution addresses, to some extent, the problems of open tips, insufficient structural stiffness, and high noise levels associated with traditional open-blade propellers, providing a new configuration approach for low-noise propellers.

[0005] However, the aforementioned annular propellers primarily improve propeller performance by closing the propeller tip and increasing overall rigidity. For low-altitude unmanned aerial vehicles (UAVs), actual operation often involves frequent hovering, acceleration, deceleration, and transitions from hovering to forward flight, resulting in continuous changes in the direction of the incoming flow and the local flow field around the propeller. Relying solely on a closed propeller tip to form a annular structure may still be insufficient to simultaneously achieve high propulsion efficiency, low noise performance, and structural simplicity under complex flight conditions.

[0006] Therefore, there is an urgent need to provide a relatively simple, high-efficiency, low-noise propeller device suitable for low-altitude unmanned aerial vehicles (UAVs), which can better adapt to the multi-condition operation requirements of low-altitude UAVs while reducing aerodynamic losses and noise caused by open propeller tips, thereby achieving a balance between propulsion efficiency, low noise performance, and operational reliability without relying on complex active pitch control mechanisms. Summary of the Invention

[0007] The purpose of this application is to provide a ring propeller device and an aircraft in order to address the shortcomings of the prior art.

[0008] To achieve the above objectives, the technical solution adopted in this application is as follows: In one aspect, this application provides an annular propeller device, including a hub, a high-position blade pair and a low-position blade pair, wherein the hub has a hub axis and a rotation reference plane perpendicular to the hub axis, and the rotation reference plane is located between the high-position blade pair and the low-position blade pair. The high-position blade pair includes two high-position blade sections arranged circumferentially along the hub, and the low-position blade pair includes two low-position blade sections arranged circumferentially along the hub. Each high-position blade section and each low-position blade section has a root end close to the hub and an outer end away from the hub. The high-position blade section and the low-position blade section are connected to the hub through their respective root ends and rotate synchronously with the hub around the hub axis. The outer end of each high-position blade section is connected to the outer end of the adjacent low-position blade section along the circumferential direction of the hub through a blade tip connecting section, so that the high-position blade section, the low-position blade section and the blade tip connecting section together form an annular blade structure with a closed blade tip. The high-position blade pair and the low-position blade pair are located on opposite sides of the rotating reference plane, so that an axial offset distance is formed between the high-position blade pair and the low-position blade pair along the hub axis. Both the high-position blade section and the low-position blade section have a geometric pitch angle that varies from the root end to the outer end. At the same radial position from the hub axis, the geometric pitch angle of the low-position blade section is greater than that of the high-position blade section, and the difference in geometric pitch angle between the low-position blade section and the high-position blade section gradually increases from the root end to the outer end.

[0009] Furthermore, the two high-position blade sections are arranged 180° apart along the circumference of the hub, and the two low-position blade sections are arranged 180° apart along the circumference of the hub, with the high-position blade sections and low-position blade sections alternating sequentially along the circumference of the hub.

[0010] Furthermore, the axial distance from the high-position blade section to the rotating reference plane gradually increases from the root end to the outer end, and the axial distance from the low-position blade section to the rotating reference plane gradually increases from the root end to the outer end.

[0011] Furthermore, at the same radial position from the hub axis, the axial offset distance between the high-position blade section and the low-position blade section gradually increases from the root end to the outer end.

[0012] Furthermore, the maximum axial offset distance between the high-position blade section and the low-position blade section along the hub axis is 0.05 to 0.2 times the blade radius, where the blade radius is the distance from the hub axis to the outermost radial contour of the annular blade structure.

[0013] Furthermore, the blade tip connecting section extends circumferentially from the outer end of the high-position blade section toward the outer end of the adjacent low-position blade section along the hub, and bends and transitions along the hub axis from the side where the high-position blade section is located to the side where the low-position blade section is located; the blade tip connecting section has a transition pitch angle that continuously changes from the geometric pitch angle of the outer end of the high-position blade section it connects to to the geometric pitch angle of the outer end of the low-position blade section.

[0014] Furthermore, the high-position blade section, the low-position blade section, and the tip connection section all have a leading edge, a trailing edge, a pressure surface, and a suction surface; the leading edge of the tip connection section smoothly transitions to the leading edges of the high-position blade section and the low-position blade section to which it is connected; the trailing edge of the tip connection section smoothly transitions to the trailing edges of the high-position blade section and the low-position blade section to which it is connected; the pressure surface of the tip connection section smoothly transitions to the pressure surfaces of the high-position blade section and the low-position blade section to which it is connected; and the suction surface of the tip connection section smoothly transitions to the suction surfaces of the high-position blade section and the low-position blade section to which it is connected.

[0015] Furthermore, both the high-position blade section and the low-position blade section are variable airfoil blade sections. Both the high-position blade section and the low-position blade section have multiple airfoil sections along their respective root-to-outer-end direction. The chord length of the multiple airfoil sections gradually decreases from the root-to-outer-end, and at least one of the camber and thickness of the multiple airfoil sections gradually decreases from the root-to-outer-end.

[0016] Furthermore, the geometric pitch angles of both the high-position blade section and the low-position blade section gradually decrease from the root end to the outer end, and the decrease in the geometric pitch angle of the high-position blade section is greater than that of the low-position blade section.

[0017] In another aspect of this application, an aircraft is provided, including a fuselage, a drive mechanism, and at least one of the aforementioned annular propeller devices. The annular propeller device is mounted on the fuselage, and the drive mechanism is connected to the hub of the annular propeller device to drive the hub to rotate around the hub axis.

[0018] The beneficial effects of this application include: This application provides an annular propeller device, which forms an annular blade structure with a closed tip by a high-position blade section, a low-position blade section, and a tip connecting section. This replaces the discrete open tip in traditional open propellers with a continuously connected tip structure. This structure alters the path of the airflow from the high-pressure side to the low-pressure side at the outer end of the blade, weakening the concentrated tip vortex that easily forms at the open tip, thereby reducing induced losses and aerodynamic noise caused by tip vortices, and improving the structural continuity and operational safety of the outer blade region.

[0019] This application arranges the high-position blade pair and the low-position blade pair on opposite sides of the rotating reference plane, creating an axial offset between them along the hub axis. This staggered arrangement positions the high-position and low-position blade sections in different spatial flow fields during rotation, reducing the direct interference of the wake, downwash, and velocity deficit generated by one type of blade section on the other. Compared to a coplanar annular propeller, this application improves the local inflow conditions of the low-position blade section, making the aerodynamic effects of the high-position and low-position blade sections more coordinated, thereby enhancing the thrust performance and aerodynamic stability of the annular propeller during hovering, forward flight, and transitional flight conditions.

[0020] This application further ensures that the geometric pitch angle of the lower blade section is greater than that of the upper blade section at the same radial position, and that the difference in geometric pitch angle between the two gradually increases from the root end to the outer end. This arrangement can compensate for the changes in the inflow angle caused by the downwash and wake disturbance induced by the upper blade section in the flow field where the lower blade section is located, allowing the lower blade section to maintain a more suitable effective operating angle at different radial positions. Especially in the high-speed region on the outer side of the blade, the gradually increasing pitch angle difference can improve the local aerodynamic matching relationship and reduce the risk of insufficient thrust or airflow separation.

[0021] The blade tip connection section of this application achieves circumferential connection and axial bending transition between the outer ends of the upper and lower blade sections, and its transition pitch angle can continuously change from the geometric pitch angle of the outer end of the upper blade section to the geometric pitch angle of the outer end of the lower blade section. Through this configuration, the closed blade tip region not only achieves structural connection but also enables a smoother aerodynamic shape transition, avoiding abrupt pitch angle changes at the outer end connection, thereby reducing local flow separation, additional drag, and vortex concentration near the blade tip connection section.

[0022] This application improves the aerodynamic interference between the blade tip vortex structure and the blade sections by combining closed blade tips, vertical and horizontal axial misalignment, differentiated geometric pitch angle distribution, and variable airfoil blade sections, without relying on active pitch control mechanisms or complex variable geometry mechanisms. Therefore, this application can achieve low noise, thrust performance, and aerodynamic efficiency while maintaining a relatively simple structure, making it more suitable for low-altitude unmanned aerial vehicles (UAVs) in noise-sensitive scenarios such as urban delivery and inspection monitoring. Attached Figure Description

[0023] Figure 1 This is one of the structural schematic diagrams of a ring-shaped propeller device provided in this application; Figure 2 This is the second schematic diagram of a ring-shaped propeller device provided in this application; Figure 3 A schematic diagram of the lateral structure of a ring-shaped propeller device under a flow field, provided for this application; Figure 4 This application provides a schematic diagram of the airfoil cross-sectional distribution of an annular propeller device; Figure 5 Comparison of streamline cloud diagrams based on turbulent kinetic energy and vorticity for an open-type propeller and a ring-shaped propeller device provided in this application; Figure 6 A thrust comparison diagram of an annular propeller device with no axial offset and an annular propeller device with different axial offset distances provided in this application; Figure 7 Comparison of vortex streamline cloud diagrams of an annular propeller device without axial offset and an annular propeller device with axial offset distance provided in this application.

[0024] Reference numerals: 1-hub; 2-high-position blade section; 3-low-position blade section; 4-circumferential offset angle; 5-axial offset distance; 6-tip connection section; 7a-outer radius of the loop; 7b-inner radius of the loop; 8-center point of the annular loop; 9a-forward sweep of the blade; 9b-backward sweep of the blade; 10-predetermined rotation direction. Detailed Implementation

[0025] like Figure 1 and Figure 2As shown, this embodiment provides a ring propeller device, which can be used as a lift-generating component or a propulsion component for low-altitude unmanned aerial vehicles (UAVs), and is particularly suitable for multi-rotor UAVs in hovering, forward flight, and transitional flight conditions between hovering and forward flight. The ring propeller device includes a hub 1, a high-mounted blade pair, and a low-mounted blade pair. The hub 1 is used to connect to the vehicle's drive mechanism and serves as the mounting base for each blade section. The hub 1 has a hub axis, which is the rotation center axis of the ring propeller device during operation. A plane perpendicular to the hub axis is a rotation reference plane, which defines the relative positions of the high-mounted and low-mounted blade pairs in the direction of the hub axis, and is not limited to the ground horizontal plane when the vehicle is in a certain attitude.

[0026] In this embodiment, to avoid ambiguity in the understanding of direction, the directional references in the annular propeller device are explained as follows: the hub axis refers to the rotational center axis of hub 1 in the working state; the axial direction refers to the direction parallel to the hub axis; the radial direction refers to the direction extending outward from the hub axis in the projection plane perpendicular to the hub axis; the circumferential direction refers to the direction of rotation around the hub axis. The root-to-outer-end direction refers to the spanwise direction in which the blade segment extends from the end closer to hub 1 to the end farther from hub 1. It can be consistent with the strictly radial direction, or it can be at an angle to the radial direction due to forward sweep, backward sweep, or curved shape. In this text, "at the same radial position as the hub axis" means a position with the same radial distance from the projection point of the hub axis in the projection plane perpendicular to the hub axis.

[0027] In this embodiment, the predetermined rotation direction refers to the direction in which the annular propeller device rotates around the hub axis under designed operating conditions. The circumferential offset angle 4 can be understood as the angle formed around the hub axis between the blade centerline or its reference radial line of the higher blade section 2 and the blade centerline or its reference radial line of the adjacent lower blade section 3 in a projection plane perpendicular to the hub axis.

[0028] In this paper, the leading and trailing edges are determined based on the local relative inflow direction of the annular propeller assembly under predetermined rotation and inflow conditions. The leading edge is the edge region where the local airflow first contacts the blade, and the trailing edge is the edge region where the airflow leaves the local cross-section of the blade. The pressure surface and suction surface are the two sides of the local airfoil cross-section of the blade used to generate aerodynamic forces, respectively. Under design operating conditions, the pressure surface is usually the side with relatively higher pressure, and the suction surface is usually the side with relatively lower pressure. The above directional references are only used to illustrate the relative positional relationships between the various structures and are not limited by the actual attitude of the aircraft, the installation orientation, or the direction of ground gravity.

[0029] like Figure 1 and Figure 2As shown, the high-position blade pair and the low-position blade pair are respectively connected to the hub 1 and can rotate synchronously with the hub 1 around the hub axis. The high-position blade pair includes two high-position blade sections 2 arranged circumferentially around the hub 1, and the low-position blade pair includes two low-position blade sections 3 arranged circumferentially around the hub 1. Each high-position blade section 2 and each low-position blade section 3 has a root end close to the hub 1 and an outer end away from the hub 1. The high-position blade section 2 and the low-position blade section 3 are respectively connected to the hub 1 through their respective root ends, so that when the hub 1 rotates, it can drive the high-position blade section 2 and the low-position blade section 3 to rotate synchronously, thereby enabling the annular propeller device to generate aerodynamic force as a whole.

[0030] like Figure 1 and Figure 2 As shown, the two high-position blade sections 2 can be arranged 180° apart along the circumference of the hub 1, and the two low-position blade sections 3 can also be arranged 180° apart along the circumference of the hub 1. The high-position blade sections 2 and low-position blade sections 3 are arranged alternately along the circumference of the hub 1, so that two adjacent blade sections along the circumference of the hub 1 belong to the high-position blade pair and the low-position blade pair, respectively. This arrangement is beneficial for the annular propeller device to have a more balanced mass distribution and aerodynamic load distribution during rotation, and to reduce unbalanced vibration during high-speed rotation. The low-position blade pair can be offset by a predetermined angle relative to the high-position blade pair along the circumference of the hub 1, thereby forming a circumferential offset angle 4. This circumferential offset angle 4 can be determined according to the number of blades, the planar profile of the annular blade structure, the extension length of the blade tip connecting section 6, and the aerodynamic matching relationship between the high-position blade section 2 and the low-position blade section 3. In one specific embodiment, the circumferential offset angle 4 can be from 30° to 90°; in a preferred embodiment, the circumferential offset angle 4 can be from 45° to 75°; in the symmetrical double-ring configuration, the circumferential offset angle 4 can be set to about 60° or about 90° to take into account the connection length of the tip connection section 6, the planar unfolding shape of the annular blade structure, and the rotational dynamic balance.

[0031] like Figure 1 and Figure 2 As shown, the outer end of each high-position blade section 2 is connected to the outer end of the adjacent low-position blade section 3 along the circumference of the hub 1 via a blade tip connecting section 6, so that the high-position blade section 2, the low-position blade section 3, and the blade tip connecting section 6 together form an annular blade structure with a closed blade tip. In this structure, the outer ends of the high-position blade section 2 and the low-position blade section 3 are not the free blade tips of a traditional open propeller, but are connected to each other through the blade tip connecting section 6. The blade tip connecting section 6 is part of the aerodynamic shape of the blade that rotates synchronously with the hub 1, and is not a protective ring, duct, or external guard fixedly set on the outer circumference of the blade. Through this closed blade tip configuration, the path of the high-pressure side airflow directly bypassing to the low-pressure side at the traditional open blade tip is changed, and the concentrated blade tip vortex that is easily formed near the open blade tip is weakened, thereby helping to reduce induced losses and aerodynamic noise caused by the shedding of strong coherent vortices.

[0032] like Figure 1 and Figure 3 As shown, the high-position blade pair and the low-position blade pair are located on opposite sides of the rotating reference plane, creating an axial offset distance 5 between them along the hub axis. In other words, the high-position blade pair and the low-position blade pair are not coplanar structures located in the same rotating plane, but rather are misaligned along the hub axis. This misalignment places the high-position blade section 2 and the low-position blade section 3 in different spatial flow field positions during operation, which helps to reduce the direct interference between the two types of blade sections caused by wake velocity deficit, local downwash, and vortex interaction. Compared to coplanar annular blades, this axially misaligned arrangement allows the low-position blade section 3 to obtain smoother local inflow conditions, enabling both the high-position blade section 2 and the low-position blade section 3 to generate aerodynamic force more stably during rotation.

[0033] like Figure 3 As shown, in this embodiment, positive and negative axial offsets can be defined based on the rotational reference plane and the hub axis direction. A positive axial offset is defined when the higher blade pair is located on one side of the rotational reference plane along the positive direction of the hub axis and the lower blade pair is located on one side of the rotational reference plane along the negative direction of the hub axis; a negative axial offset is defined when the higher blade pair is located on one side of the rotational reference plane along the negative direction of the hub axis and the lower blade pair is located on one side of the rotational reference plane along the positive direction of the hub axis. The positive and negative directions described above only describe the axial arrangement direction of the higher and lower blade pairs relative to the rotational reference plane and do not change the technical meaning of the axial offset distance 5 formed between them along the hub axis direction. Depending on the aircraft installation direction, propeller rotation direction, and incoming flow direction, both positive and negative axial offsets can be used to improve the aerodynamic interference between the higher blade section 2 and the lower blade section 3.

[0034] like Figure 1 and Figure 3As shown, the axial distance from the high-position blade section 2 to the rotating reference plane can gradually increase from the root end to the outer end, and the axial distance from the low-position blade section 3 to the rotating reference plane can also gradually increase from the root end to the outer end. Since the high-position blade pair and the low-position blade pair are located on opposite sides of the rotating reference plane, the above arrangement results in a smaller axial misalignment between the high-position blade section 2 and the low-position blade section 3 near the hub 1, and a larger axial misalignment far from the hub 1. This not only ensures a good structural connection and load transfer between the root end of each blade section and the hub 1, but also creates a more obvious high-low misalignment effect in the outer region of the blades. Since the local linear velocity in the outer region of the blades is higher, the aerodynamic disturbances generated in the outer region and the airflow between adjacent blade sections have a more significant interaction. Therefore, gradually increasing the axial offset distance 5 from the root end to the outer end helps the outer region of the low-position blade section 3 avoid the strong disturbance flow field generated in the outer region of the high-position blade section 2, improving the local inflow conditions of the low-position blade section 3.

[0035] like Figures 1 to 3 As shown, in one specific embodiment, the maximum axial offset distance 5 between the high-position blade section 2 and the low-position blade section 3 along the hub axis can be 0.05 to 0.2 times the blade radius. The blade radius can be understood as the maximum distance from the projection point of the hub axis to the outermost projected profile of the annular blade structure in a projection plane perpendicular to the hub axis. By controlling the maximum axial offset distance 5 within the above range, the aerodynamic interference between the high-position blade section 2 and the low-position blade section 3 can be reduced, while avoiding the difficulty in effectively separating the wake interference area due to excessively small axial misalignment, and also avoiding the increase in the overall axial dimension of the annular propeller device, excessively sharp bending of the blade tip connection section 6, or a significant increase in structural load due to excessively large axial misalignment. In a preferred embodiment, the maximum axial offset distance 5 can be 0.08 to 0.15 times the blade radius; in the application scenario of small low-altitude unmanned aerial vehicles, the maximum axial offset distance 5 can be 0.10 to 0.12 times the blade radius, so as to balance the aerodynamic improvement effect, structural compactness, and manufacturing difficulty.

[0036] In one specific embodiment, the overall diameter of the annular propeller assembly can be 177.8 mm, and the diameter of the hub 1 can be 20 mm. For this type of propeller for small low-altitude unmanned aerial vehicles, the maximum axial offset distance 5 between the upper blade section 2 and the lower blade section 3 can be selected within the aforementioned range based on the blade radius, and the maximum geometric pitch angle difference between the lower blade section 3 and the upper blade section 2 can be set to approximately 10°. The above dimensions and angles are only used to illustrate a specific embodiment suitable for small unmanned aerial vehicles and do not limit the application of the annular propeller assembly in other blade diameters, other hub sizes, or other aircraft platforms.

[0037] like Figures 1 to 3As shown, the blade tip connecting section 6 extends circumferentially from the outer end of the high-position blade section 2 toward the outer end of the adjacent low-position blade section 3 along the hub 1, and bends along the hub axis from the side where the high-position blade section 2 is located to the side where the low-position blade section 3 is located. In other words, the blade tip connecting section 6 not only completes the connection between the outer ends of adjacent blade sections circumferentially, but also completes the transition between the high-position and low-position positions axially. Through this spatial bending transition structure, the high-position blade section 2, the low-position blade section 3, and the blade tip connecting section 6 can form a continuous closed blade tip configuration, thereby reducing free-end flow and concentrated vortex shedding at the traditional open blade tip.

[0038] like Figure 1 and Figure 4 As shown, due to the difference in geometric pitch angles between the high-position blade section 2 and the low-position blade section 3, the blade tip connecting section 6 can have a transition pitch angle. This transition pitch angle continuously changes from the geometric pitch angle at the outer end of the high-position blade section 2 to the outer end of the low-position blade section 3. Through this continuous pitch angle change, the blade tip connecting section 6 can simultaneously adapt to the different pitch angles of the high-position blade section 2 and the low-position blade section 3 in its aerodynamic shape, avoiding abrupt angle changes in the outer end connection area. This helps reduce local flow separation and additional drag near the blade tip connecting section 6, resulting in a smoother airflow transition in the closed blade tip region during rotation.

[0039] like Figure 1 and Figure 4 As shown, the high-position blade section 2, the low-position blade section 3, and the tip connecting section 6 can all have a leading edge, a trailing edge, a pressure surface, and a suction surface. The leading edge is the edge region where the local airflow first contacts the blade, and the trailing edge is the edge region where the airflow leaves the local cross-section of the blade. The pressure surface and suction surface are located on opposite sides of the blade cross-section, collectively forming the aerodynamic shape of the blade. The leading edge of the tip connecting section 6 smoothly transitions to the leading edges of the connected high-position blade section 2 and the low-position blade section 3. Similarly, the trailing edge of the tip connecting section 6 smoothly transitions to the trailing edges of the connected high-position blade section 2 and the low-position blade section 3. Correspondingly, the pressure surface of the tip connecting section 6 smoothly transitions to the pressure surfaces of the connected high-position blade section 2 and the low-position blade section 3, and the suction surface of the tip connecting section 6 smoothly transitions to the suction surfaces of the connected high-position blade section 2 and the low-position blade section 3. Through the smooth transition connection of the leading edge, trailing edge, pressure surface and suction surface, the tip connection section 6 can form a relatively continuous spatial curved surface with the high-position blade section 2 and the low-position blade section 3, which is not easy to form abrupt boundary or local angle at the connection, thus helping to reduce local pressure abruptness, eddy current concentration and structural stress concentration.

[0040] like Figure 2As shown, in the projection plane perpendicular to the hub axis, the annular blade structure has a center point 8 of the annular loop, which is the local curvature center point of the annular blade structure. The distance from the center point 8 of the annular loop to the outer contour of the annular blade structure forms the outer radius 7a of the loop, and the distance from the center point 8 of the annular loop to the inner contour of the annular blade structure forms the inner radius 7b of the loop. The outer radius 7a and the inner radius 7b of the loop together characterize the loop radius. Since the annular blade structure formed by the high-position blade segment 2, the low-position blade segment 3, and the tip connecting segment 6 does not necessarily have to be a standard circle, the outer radius 7a and the inner radius 7b of the loop can change along the circumference of the hub 1. That is, when the circumferential position of the tip connecting segment 6 changes, the distance from the center point of the annular loop to the outer and inner edges of the annular blade structure changes, causing the annular blade structure to present an asymmetrical or elongated closed loop shape in the projection plane.

[0041] like Figure 2 As shown, in a projection plane perpendicular to the hub axis, the blade centerlines of the high-position blade section 2 and the low-position blade section 3 can be circumferentially deflected relative to a radial reference line extending outward from the hub axis. Specifically, the blade centerline of the high-position blade section 2 can deflect towards the predetermined rotation direction, while the blade centerline of the low-position blade section 3 can deflect towards the opposite side of the predetermined rotation direction, thus forming a forward-swept section and a backward-swept section, corresponding to blade forward sweep 9a and blade backward sweep 9b, respectively. The forward and backward sweep angles of this closed annular propeller are not single fixed values ​​but are continuously varying angularly along the blade. Since the blade sections are composed of nonlinear curves, their sweep angle distribution needs to change at different local positions along the blade curve. Through the aforementioned forward and backward sweep sections, the load distribution of the blade sections in the projection plane and the connection path of the tip connection section 6 can be adjusted, and the local flow state of the annular blade structure during rotation can be improved.

[0042] like Figure 4 As shown, both the high-position blade section 2 and the low-position blade section 3 have geometric pitch angles that vary from the root end to the outer end. The geometric pitch angle can be understood as the installation tilt angle of the local airfoil section of the blade section relative to the rotating reference plane; its magnitude affects the direction and intensity of the blade section's action on the air during rotation. At the same radial position from the hub axis, the geometric pitch angle of the low-position blade section 3 is greater than that of the high-position blade section 2. This configuration allows the low-position blade section 3 to adapt to the local incoming flow direction, which is already disturbed by the high-position blade section 2 at its location. This helps compensate for the effective inflow angle changes caused by the downwash and wake disturbances, maintaining a more suitable aerodynamic operating state for the low-position blade section 3.

[0043] like Figure 4As shown, the difference in geometric pitch angle between the lower blade section 3 and the higher blade section 2 gradually increases from the root end to the outer end. This difference can be a continuous function or a piecewise continuous function. Specifically, in one embodiment, the difference in geometric pitch angle between the lower blade section 3 and the higher blade section 2 can increase linearly in the radial direction; in another embodiment, the difference in geometric pitch angle can increase slowly near the root end and increase more significantly from the middle to the outer end; in yet another embodiment, the difference in geometric pitch angle can increase using a piecewise smooth curve. All of the above variations aim to avoid abrupt changes in the geometric pitch angle. Since the closer the blade section is to the outer end, the higher its local linear velocity when rotating around the hub axis, and the more sensitive it is to changes in the local flow direction, increasing the difference in geometric pitch angle between the lower blade section 3 and the higher blade section 2 in the outer region helps the outer region of the lower blade section 3 to better adapt to the local flow field after the high-low misalignment. In one specific embodiment, the maximum geometric pitch angle difference between the lower blade section 3 and the upper blade section 2 can be 6° to 12°; in a preferred embodiment, the maximum geometric pitch angle difference can be 8° to 10°.

[0044] like Figure 4 As shown, the geometric pitch angles of both the high-position blade section 2 and the low-position blade section 3 can gradually decrease from the root end to the outer end. Since the local linear velocity in the outer region of the blade section is higher, a suitable local aerodynamic effect can be obtained in the outer region with a smaller geometric pitch angle; while the linear velocity in the root region is lower, requiring a relatively larger geometric pitch angle to improve the local work capacity. Therefore, gradually decreasing the geometric pitch angle from the root end to the outer end is beneficial for the blade section to adapt to different local linear velocity conditions in the radial direction. Furthermore, the reduction in the geometric pitch angle of the high-position blade section 2 can be greater than that of the low-position blade section 3, so that the low-position blade section 3 still maintains a larger pitch angle compensation amount in the radially outer direction relative to the high-position blade section 2, thus matching the relationship that the difference in geometric pitch angle between the low-position blade section 3 and the high-position blade section 2 gradually increases from the root end to the outer end.

[0045] like Figure 4As shown, both the high-mounted blade section 2 and the low-mounted blade section 3 can be variable airfoil blade sections. Both high-mounted blade section 2 and low-mounted blade section 3 have multiple airfoil sections along their respective root-to-outer-end direction. The chord length of these multiple airfoil sections can gradually decrease from the root to the outer end, and at least one of the camber and thickness of these multiple airfoil sections can gradually decrease from the root to the outer end. An airfoil section refers to a local aerodynamic section taken at different radial positions of the blade section. The chord length reflects the dimension of the section from the leading edge to the trailing edge, while the camber and thickness reflect the aerodynamic load-bearing capacity and structural characteristics of the section. The local linear velocity is lower in the root region near the hub 1, and the root region can obtain effective aerodynamic forces through a larger local cross-sectional size or stronger airfoil load-bearing capacity. The local linear velocity is higher in the region near the outer end, and the use of a smaller chord length, camber, or thickness in the outer end region is beneficial for reducing section drag and the risk of local flow separation. Through this variable airfoil design, the root region can maintain good low-speed work capacity, while the outer region can reduce drag and noise at high speeds, thereby improving the overall aerodynamic performance of the annular propeller device.

[0046] In terms of manufacturing method, the annular propeller assembly can be manufactured using a one-piece molding method or a segmented molding and then connecting method. Preferably, at least the aerodynamic shape of the blades in the hub 1, high-position blade section 2, low-position blade section 3, and tip connection section 6 is integrally molded to reduce connection seams, assembly errors, and local stress concentration. The annular propeller assembly can be made of carbon fiber composite materials, glass fiber composite materials, reinforced nylon, engineering plastics, or lightweight metal materials. For small low-altitude unmanned aerial vehicles, carbon fiber composite materials are preferred to balance low mass, high stiffness, and fatigue resistance. When using carbon fiber composite materials, a main load-bearing fiber layer can be provided along the length of the blade section, extending from the root end to the outer end; a circumferential fiber layer extending continuously along its bending path can be provided in the tip connection section 6 to improve the tensile and bending strength of the closed tip region; oblique fiber layers or cross-layouts can also be provided to improve the torsional stiffness of the blade section and the tip connection section 6.

[0047] When the annular propeller assembly is manufactured using a segmented molding and then joined method, the upper blade segment 2, the lower blade segment 3, and the tip connecting segment 6 can be molded separately and then connected. Adjacent components can be joined using structural adhesive bonding, lap bonding, tongue and groove bonding, mechanical fastener connection, wet-coating and curing of composite materials, or a combination of these methods. Preferably, the tip connecting segment 6 is lap-bonded to the outer ends of the upper blade segment 2 and the lower blade segment 3, and reinforced with a composite material coating layer, ensuring a smooth transition in the connecting area and providing high tensile, bending, and torsional strength. For structures using carbon fiber composite materials, the reinforcing coating layer can be continuously laid along the bending direction of the tip connecting segment 6 and extend to cover the outer ends of the upper blade segment 2 and the lower blade segment 3 to reduce the risk of peeling and fatigue damage at the connection interface.

[0048] The root ends of the high-position blade section 2 and the low-position blade section 3 can be integrally formed with the hub 1, or they can be connected to the hub 1 through inserts, connecting seats, adhesive layers, screws, rivets, or composite material coverings. Preferably, a root transition reinforcement is provided between the root end of the blade section and the hub 1. The root transition reinforcement can adopt a thickened transition, a rounded transition, a reinforcing fiber layer, or a partial sandwich structure to improve the load-bearing capacity of the connection area between the root end and the hub 1. A reinforcement layer can also be provided in the connection area between the high-position blade section 2, the low-position blade section 3, and the blade tip connection section 6. This reinforcement layer extends along the outer end of the blade section and the blade tip connection section 6, and covers at least a portion of the pressure surface and suction surface of the connection area to improve the bending, torsional, and fatigue resistance of the connection between the blade tip connection section 6 and the blade section.

[0049] Because the high-position blade section 2 and the low-position blade section 3 in this embodiment are axially offset along the hub axis, and the blade tip connection section 6 forms a spatial bending connection, the blade section may be subjected to centrifugal loads, aerodynamic loads, and torsional loads during high-speed rotation. To reduce torsional deformation under high-speed rotation, the overall torsional resistance can be improved by increasing the root thickness of the blade section, setting anti-torsional ply, increasing the local cross-sectional stiffness of the blade tip connection section 6, optimizing the fillet radius at the connection between the blade section and the hub 1, and arranging a continuous fiber reinforcement layer in the blade tip connection section 6. During the design process, static strength and modal checks can be performed on the blade section according to the target rotational speed and target thrust to ensure that its operating speed avoids the main natural frequency range and reduces the risk of resonance.

[0050] To ensure the stability of the annular propeller assembly during high-speed rotation, mass balancing and dynamic balancing correction can be performed after manufacturing. Dynamic balancing correction may include detecting the mass distribution on both sides of the hub axis, detecting the circumferential mass difference between the high-position blade section 2 and the low-position blade section 3, and detecting local mass deviations in the tip connection section 6. Imbalance can be reduced by locally removing material, adding counterweights, adjusting the surface coating thickness, or correcting the mass distribution in the hub 1 connection area. For annular propeller assemblies manufactured using composite materials, a three-dimensional scan of the blade shape can be performed after curing to verify the axial offset distance 5 between the high-position blade section 2 and the low-position blade section 3, the geometric pitch angle distribution, and the surface continuity of the tip connection section 6, ensuring that the actual formed shape meets design requirements.

[0051] like Figure 5 As shown, to verify the flow field improvement effect of the annular propeller device, numerical simulations can be performed to compare open propellers, annular propellers without axial offset, and annular propellers with axial offset. Under the same rotational speed, the same incoming flow conditions, and the same air density, the open propeller tends to form a concentrated vortex structure and a high turbulent kinetic energy region near the tip. After adopting the annular blade structure with a closed tip, the concentrated vortex structure near the tip is weakened, and the wake flow field tends to be dispersed. Therefore, its potential to reduce aerodynamic noise can be indirectly judged from the vorticity distribution and turbulent kinetic energy distribution. For further confirmation of noise performance, it can be evaluated in subsequent experiments or simulations through sound pressure level, spectral distribution, blade passing frequency and its harmonic components.

[0052] like Figure 6 As shown, under the same simulation conditions, the thrust of a ring propeller without axial offset can be compared with that of a ring propeller with different axial offset amplitudes. For example, the thrust of the structure without axial offset is approximately 12.8 N; when the axial offset amplitude is +6% and -6% of the blade radius, the thrust is approximately 13.93 N and 14 N, respectively; when the axial offset amplitude is +8% and -8% of the blade radius, the thrust is approximately 14.81 N and 14 N, respectively; and when the axial offset amplitude is +12% and -12% of the blade radius, the thrust is approximately 17.7 N and 17.57 N, respectively. Both positive and negative axial offsets can improve thrust performance to some extent, indicating that the axial misalignment between the high-position blade section 2 and the low-position blade section 3 is beneficial to improving the aerodynamic interference between them. It should be noted that the above thrust comparison is the result obtained under specific simulation conditions, and an increase in thrust does not necessarily equate to a proportional increase in propulsion efficiency; propulsion efficiency is also related to input power, torque, rotational speed, incoming flow velocity, and operating conditions. Therefore, the above simulation results are mainly used to illustrate that the axial offset structure can improve aerodynamic working conditions and thrust performance, and can serve as a basis for further optimizing propulsion efficiency and low noise performance.

[0053] like Figure 7 As shown, a comparison of vorticity streamlines reveals that in the structure without axial offset, the strong vortex regions between the high-position blade section 2 and the low-position blade section 3 are more easily coupled directly, resulting in significant distortion of streamlines between adjacent blade sections. With the axial offset structure, the strong disturbance region generated by the high-position blade section 2 is spatially separated from the main working region of the low-position blade section 3, leading to a smoother local flow field through the low-position blade section 3 and a reduced concentration of the high vorticity region. This result further demonstrates that the combination of the axial offset distance 5 and the differentiated geometric pitch angle distribution is beneficial for improving the aerodynamic operating state of the annular propeller device under transitional flight conditions.

[0054] This embodiment also provides an aircraft. The aircraft includes a fuselage, a drive mechanism, and at least one of the aforementioned annular propeller devices. The annular propeller device is mounted on the fuselage, and the drive mechanism is kinetically connected to the hub 1 of the annular propeller device to drive the hub 1 to rotate around the hub axis. The drive mechanism can be a motor, and the motor output shaft can be directly connected to the hub 1, or it can be connected to the hub 1 through a reduction mechanism, coupling, or mounting base. The drive mechanism drives the hub 1, the high-position blade pair, the low-position blade pair, and the blade tip connecting section 6 to rotate synchronously, so that the annular propeller device generates lift or thrust for the flight of the aircraft.

[0055] When an aircraft employs multiple annular propeller units, these units can be distributed across different locations on the fuselage to meet the needs of vertical takeoff and landing, hovering, attitude control, or forward propulsion. These annular propeller units can be mounted on the main fuselage body, arms, motor mounts, or supporting structures connected to the fuselage. Due to the closed-tip structure, staggered blade arrangement, and differentiated pitch angle distribution of this annular propeller unit, the aircraft can improve the local flow field near the propeller while maintaining a relatively simple structure during hovering, forward flight, and hovering-to-forward flight transitions. This reduces aerodynamic noise and safety risks associated with open propeller tips and enhances the stability of the propulsion or lift generation process.

[0056] Furthermore, since the aircraft uses the aforementioned annular propeller device, it also has the same beneficial effects as the annular propeller device, which will not be elaborated here.

[0057] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A ring-shaped propeller device, characterized in that, It includes a hub, a high-position blade pair and a low-position blade pair. The hub has a hub axis and a rotation reference plane perpendicular to the hub axis. The rotation reference plane is located between the high-position blade pair and the low-position blade pair. The high-position blade pair includes two high-position blade sections arranged circumferentially along the hub, and the low-position blade pair includes two low-position blade sections arranged circumferentially along the hub. Each high-position blade section and each low-position blade section has a root end close to the hub and an outer end away from the hub. The high-position blade section and the low-position blade section are connected to the hub through their respective root ends and rotate synchronously with the hub around the hub axis. The outer end of each high-position blade section is connected to the outer end of the adjacent low-position blade section along the circumferential direction of the hub through a blade tip connecting section, so that the high-position blade section, the low-position blade section and the blade tip connecting section together form an annular blade structure with a closed blade tip. The high-position blade pair and the low-position blade pair are located on opposite sides of the rotating reference plane, so that an axial offset distance is formed between the high-position blade pair and the low-position blade pair along the hub axis. Both the high-position blade section and the low-position blade section have a geometric pitch angle that varies from the root end to the outer end. At the same radial position from the hub axis, the geometric pitch angle of the low-position blade section is greater than that of the high-position blade section, and the difference in geometric pitch angle between the low-position blade section and the high-position blade section gradually increases from the root end to the outer end.

2. The annular propeller device according to claim 1, characterized in that, Two high-position blade sections are arranged 180° apart along the circumference of the hub, and two low-position blade sections are arranged 180° apart along the circumference of the hub, with the high-position blade sections and low-position blade sections alternating sequentially along the circumference of the hub.

3. The annular propeller device according to claim 1, characterized in that, The axial distance from the high-position blade section to the rotating reference plane gradually increases from the root end to the outer end, and the axial distance from the low-position blade section to the rotating reference plane gradually increases from the root end to the outer end.

4. The annular propeller device according to claim 1, characterized in that, At the same radial position as the hub axis, the axial offset distance between the high-position blade section and the low-position blade section gradually increases from the root end to the outer end.

5. The annular propeller device according to claim 1, characterized in that, The maximum axial offset distance between the high-position blade section and the low-position blade section along the hub axis is 0.05 to 0.2 times the blade radius, which is the distance from the hub axis to the outermost radial contour of the annular blade structure.

6. The annular propeller device according to claim 1, characterized in that, The blade tip connecting section extends circumferentially from the outer end of the high blade section toward the outer end of the adjacent low blade section, and bends and transitions along the hub axis from the side where the high blade section is located to the side where the low blade section is located; the blade tip connecting section has a transition pitch angle that changes continuously from the geometric pitch angle of the outer end of the high blade section it connects to to the geometric pitch angle of the outer end of the low blade section.

7. The annular propeller device according to claim 1, characterized in that, The high-position blade section, low-position blade section, and tip connection section all have a leading edge, a trailing edge, a pressure surface, and a suction surface. The leading edge of the tip connection section smoothly transitions to the leading edges of the high-position blade section and the low-position blade section it connects to. The trailing edge of the tip connection section smoothly transitions to the trailing edges of the high-position blade section and the low-position blade section it connects to. The pressure surface of the tip connection section smoothly transitions to the pressure surfaces of the high-position blade section and the low-position blade section it connects to. The suction surface of the tip connection section smoothly transitions to the suction surfaces of the high-position blade section and the low-position blade section it connects to.

8. The annular propeller device according to claim 1, characterized in that, Both the high-position blade section and the low-position blade section are variable airfoil blade sections. Both the high-position blade section and the low-position blade section have multiple airfoil sections along their respective root end to outer end. The chord length of the multiple airfoil sections gradually decreases from the root end to the outer end, and at least one of the camber and thickness of the multiple airfoil sections gradually decreases from the root end to the outer end.

9. The annular propeller device according to any one of claims 1 to 8, characterized in that, The geometric pitch angles of both the high-position blade section and the low-position blade section gradually decrease from the root end to the outer end, and the decrease in the geometric pitch angle of the high-position blade section is greater than that of the low-position blade section.

10. An aircraft, characterized in that, It includes a fuselage, a drive mechanism, and at least one annular propeller device as described in any one of claims 1 to 9, wherein the annular propeller device is mounted on the fuselage, and the drive mechanism is connected to the hub of the annular propeller device to drive the hub to rotate about the hub axis.

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