A noise reduction structure for a rotary-wing UAV derived from a symmetrical airfoil

Abstract

The present invention discloses a noise reduction structure for a rotary-wing UAV derived from a symmetrical airfoil. The rotary-wing UAV comprises a fuselage, a connecting rod, a motor, and a rotor, wherein the motor drives the rotor to rotate. A noise reduction pipe is fixedly arranged on the periphery of the rotor and concentric with the rotor. The pipe body of the noise reduction pipe is an annular pipe with an inlet and an outlet. The external shape of the pipe body includes an inlet lip shape, an inner cavity shape, and an outer edge shape. The inlet lip shape of the pipe body is semicircular, the inner cavity shape of the pipe body is a cylindrical cavity shape, and the outer edge shape of the pipe body is derived from the symmetrical airfoil. The present invention has a simple structure, is easy to process, has low cost, does not require the addition of additional sound-absorbing materials or sound insulation structures, and relies on the pipe's own structure to effectively reduce UAV noise, improve UAV safety, and increase UAV lift.

Description

Technical Field

[0001] The present invention relates to the technical field of rotary-wing UAVs, and more particularly to a noise reduction structure for a small rotary-wing UAV. Background Art

[0002] Small rotor drones are currently used in fields such as aerial logistics and transportation, and often operate in crowded places. However, their aerodynamic noise has become noise pollution, and their exposed blades pose a huge safety hazard, which in turn brings performance stability issues.

[0003] A Chinese patent application document with publication number CN208412125U discloses a duct structure for a UAV with a noise reduction function. A sound-absorbing layer is provided in the duct and a sound-insulating cavity is provided on the inner wall. However, the duct structure is complex and difficult to process.

[0004] A Chinese patent application document with publication number CN107614379A discloses a shield for an aircraft, which is installed in a quad-rotor drone. The inner wall of the shield is provided with ridged electrospun nanomaterials for absorbing noise, and a sound deflector is arranged to eliminate noise through reflection and refraction. However, it has problems with its complex structure and high cost, making it difficult to apply in engineering. Summary of the Invention

[0005] The present invention is to avoid the shortcomings of the above-mentioned existing technologies and provide a rotor UAV noise reduction structure derived from a symmetrical airfoil that is simple in structure, easy to implement, and does not require the addition of a sound-absorbing material layer or a sound insulation structure, thereby achieving effective noise reduction of the rotor UAV at a low cost.

[0006] The present invention adopts the following technical solutions to solve the technical problems:

[0007] The noise reduction structure of a rotor UAV derived from a symmetrical airfoil of the present invention comprises a fuselage, four connecting rods fixedly connected in a "cross" shape in the circumferential direction of the fuselage, a motor base is fixedly arranged at the distal end of each connecting rod, a motor is installed in the motor base, a rotor is fixedly installed at the upper end of the motor's rotating shaft by using a clamping cap, and the rotor is driven to rotate by the motor; the structure is characterized in that a noise reduction pipe is fixedly arranged on the periphery of the rotor and in a concentric position with the rotor; the pipe body of the noise reduction pipe is an annular pipe with an inlet and an outlet passing therethrough, the external shape of the pipe body comprises an inlet lip shape, an inner cavity shape and an outer edge shape; the inlet lip shape of the pipe body is semicircular; the inner cavity shape of the pipe body is a cylindrical cavity shape; the outer edge shape of the pipe body is derived from the symmetrical airfoil.

[0008] The noise reduction structure of the rotor UAV derived from the symmetrical airfoil of the present invention is also characterized in that: the noise reduction pipe has three support arms evenly distributed circumferentially at the bottom of its pipe body, one end of the support arm is fixedly connected to the pipe body, and the other end of the support arm is connected to the pipe base, and the pipe base is a sleeve mounted on the motor base.

[0009] The noise reduction structure of the rotor UAV derived from the symmetrical airfoil of the present invention is also characterized in that a slider and a slide groove are used as a connection method between the support arm and the pipe base, the slider is fixedly connected to the end of the support arm, and a slide groove is axially arranged at the corresponding position of the pipe base, and the slider can be slidably assembled in the slide groove and obtain axial locking.

[0010] The noise reduction structure of the rotary wing UAV derived from the symmetrical airfoil of the present invention is also characterized in that: the axial locking is achieved by providing ratchets on the sides of the slider and the slide groove, and utilizing the ratchets for axial locking.

[0011] The noise reduction structure of the rotary wing UAV derived from the symmetrical airfoil of the present invention is also characterized in that: the outer edge shape of the tube body is formed by rotating the outer edge curve, and the rotation axis is the central axis of the tube body; the outer edge curve is formed by connecting a curved segment and a straight segment;

[0012] Establish coordinate system A: the semicircular vertex of the inlet lip is the coordinate origin O, the axial direction from the tube inlet to the outlet is the positive direction of the x-axis, and the radial direction from the inner wall of the tube to the outer wall of the tube is the positive direction of the y-axis;

[0013] The equation of the curve segment in the coordinate system A is as follows:

[0014]

[0015] In formula (1):

[0016] The y-axis coordinate of the curve segment is represented by y, and the value range of y is [-0.5d, 0.5d], where positive and negative represent the direction;

[0017] d is the semicircular diameter of the inlet lip along the center axis of the tube;

[0018] A, B, C, D and E are constants, which are obtained by fitting the airfoil based on ideal flow theory and wind tunnel experimental data;

[0019] They are: A = 0.297, B = -0.126, C = -0.352, D = 0.284, E = -0.102;

[0020] X is the normalized result of the airfoil chord length, and the value of X is represented by formula (2):

[0021]

[0022] In formula (2):

[0023] The x-axis coordinate of the curve segment is represented by x, and the value range of x is [0.5d+0.3L,L];

[0024] L is the chord length, which is the axial height of the tube body. The chord length L is represented by formula (3):

[0025]

[0026] In formula (3):

[0027] R1 is the inner radius of the tube body, and the inner radius of each part is consistent;

[0028] One end of the straight line segment is connected to the semicircular portion of the inlet lip, and the other end is connected to the curved line segment. The length of the straight line segment is L1, where L1 = 0.3L.

[0029] The noise reduction structure of the rotary wing UAV derived from the symmetrical airfoil of the present invention is also characterized by:

[0030] Will The values ​​are:

[0031] The tip clearance S is taken as

[0032] The tip clearance S refers to the gap between the rotor tip and the inner cavity wall of the tube body.

[0033] Compared with the existing technology, the beneficial effects of the present invention are embodied in:

[0034] 1. The present invention has a simple structure, is easy to process, and has low cost. It does not require any sound-absorbing materials and relies on the pipe's own structure to effectively reduce the aerodynamic noise of the UAV rotor.

[0035] 2. The rotor sheath of the present invention effectively protects the rotating rotor from damage due to collision, and also avoids the potential safety hazard of high-speed rotating blades causing harm to people, thereby greatly improving safety;

[0036] 3. The present invention has excellent aerodynamic performance. In addition to the rotor, the noise reduction duct itself can generate part of the lift, which can increase the total lift by about 5%. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic diagram of the structure of the present invention;

[0038] Figure 2 This is a structural diagram of another angle of the present invention. Figure 2a It is a partial enlarged view of the present invention;

[0039] Figure 3This is a schematic diagram of the cross-sectional structure of a single duct rotor in the present invention;

[0040] Figure 4 Schematic diagram of the cross-sectional configuration of the pipeline body in the present invention;

[0041] Figure 5 The figure is a comparison of the lift curves of a single isolated rotor and a single ducted rotor in the hovering condition;

[0042] Figure 6a and Figure 6b Streamline diagrams of a single isolated rotor and a single ducted rotor in hovering conditions;

[0043] Figure 7 This is the 1 / 3 frequency diagram of a single isolated rotor and a single ducted rotor under hovering conditions. DETAILED DESCRIPTION

[0044] See also Figure 1 and Figure 2 This embodiment is a noise reduction structure for a rotary-wing UAV derived from a symmetrical airfoil. The rotary-wing UAV includes a fuselage 1, with four connecting rods 3 fixedly connected in a "cross" shape in the circumferential direction of the fuselage 1. A motor base 5 is fixedly provided at the distal end of each connecting rod. A motor 6 is installed in the motor base 5. A rotor 7 is fixedly installed at the upper end of the rotating shaft of the motor 6 using a clamping cap 9. The rotor 7 is driven to rotate by the motor 6.

[0045] The specific structural setting in this embodiment is that a noise reduction pipe 8 is fixedly arranged on the periphery of the rotor 7 and in a concentric position with the rotor 7; the pipe body 8a of the noise reduction pipe 8 is an annular pipe with an inlet and an outlet, and the external shape of the pipe body 8a includes an inlet lip shape, an inner cavity shape and an outer edge shape; the inlet lip shape of the pipe body 8a is semicircular; the inner cavity shape of the pipe body 8a is a cylindrical cavity shape; the outer edge shape of the pipe body 8a is derived from the symmetrical airfoil. The semicircular inlet lip shape helps the airflow to flow into the pipe body 8a better, ensures that the airflow flowing through is smooth and uniform, reduces the impact between the airflows and between the airflow and the pipe, and thus reduces the intensity and size of the vortex. The cylindrical cavity shape ensures uniform tip clearance and can effectively suppress the generation and development of tip vortices. The outer edge derived from the symmetrical airfoil helps the airflow near the outer wall of the pipe to flow smoothly from all sides to the downwash flow, reducing the convergence of vortices.

[0046] In specific implementation, the corresponding technical measures also include:

[0047] Figure 3The figure shows a schematic diagram of the cross-sectional structure of a single duct rotor, which shows in more detail the structural composition of the noise reduction duct 8 and the positional relationship between the various components; wherein the noise reduction duct 8 has three support arms 8b evenly distributed along the circumferential direction at the bottom of its tube body 8a, one end of the support arm 8b is fixedly connected to the tube body 8a, and the other end of the support arm 8b is connected to the duct base 8d, which is a sleeve mounted on the motor base 5.

[0048] Figure 2a for Figure 2 In the partially enlarged view, a slider and a chute are used to connect the support arm 8b and the pipe base 8d. The slider 8c is fixedly connected to the end of the support arm 8b, and a chute is set axially at the corresponding position of the pipe base 8d. The slider 8c can be slidably assembled in the chute and obtain axial locking. In a specific implementation, the axial locking can be achieved by setting ratchets on the sides of the slider and the chute, and using the ratchets to perform axial locking. The slider 8c slides in the chute, which can drive the pipe body 8a to move axially, thereby adjusting the installation position of the rotor 7 in the pipe body 8a. Its significance lies in that drones often work in different environments. Adjusting the installation position of the pipe body 8a can ensure that the drone better adapts to the surrounding flight environment and improve the stability and adaptability of the drone.

[0049] In this embodiment, the outer edge shape of the tube body 8a is formed by rotating the outer edge curve, and the rotation axis is the central axis of the tube body 8a; the outer edge curve is formed by connecting a curved segment and a straight segment.

[0050] like Figure 4 As shown, the coordinate system A is established: the semicircular vertex of the inlet lip is used as the coordinate origin O, the axial direction from the tube inlet to the outlet is used as the positive direction of the x-axis, and the radial direction from the tube cavity wall to the tube body outer wall is used as the positive direction of the y-axis; wherein C1 is the shape of the semicircular inlet lip, and C2 is the curve segment.

[0051] The equation of the curve segment in coordinate system A is as follows:

[0052]

[0053] In formula (1):

[0054] The y-axis coordinate of the curve segment is represented by y, and the value range of y is [-0.5d, 0.5d], where positive and negative represent the direction;

[0055] d is the semicircular diameter of the inlet lip along the center axis of the tube;

[0056] A, B, C, D and E are constants, which are obtained by fitting the airfoil based on ideal flow theory and wind tunnel experimental data;

[0057] They are: A = 0.297, B = -0.126, C = -0.352, D = 0.284, E = -0.102;

[0058] X is the normalized result of the airfoil chord length, and the value of X is represented by formula (2):

[0059]

[0060] In formula (2):

[0061] The x-axis coordinate of the curve segment is represented by x, and the value range of x is [0.5d+0.3L,L];

[0062] L is the chord length, which is the axial height of the tube body. The chord length L is represented by formula (3):

[0063]

[0064] In formula (3):

[0065] R1 is the inner radius of the tube body, and the inner radius of each part is consistent;

[0066] One end of the straight line segment is connected to the semicircular portion of the inlet lip, and the other end is connected to the curved segment. Its length is L1, where L1 = 0.3L. The values ​​are: The tip clearance S is taken as Tip clearance S refers to the gap between the rotor tip and the inner wall of the tube body.

[0067] like Figure 5 The figure shows a comparison of lift curves for a single isolated rotor and a ducted rotor. Curve a represents the lift variation for a single isolated rotor, while curve b represents the lift variation for a single ducted rotor. This comparison shows that after 500 iterations, the lift generated by the isolated rotor reaches 2.03 N, while the total lift generated by the ducted rotor is 2.13 N, a lift increase of approximately 5%.

[0068] Figure 6a is the streamline diagram of the isolated rotor, Figure 6b The figure shows the streamlines of the ducted rotor. A comparative analysis shows that both types of rotors generate vortices near the rotors. The airflow near the isolated rotor has a large space and a high degree of freedom, which makes it easy to generate more vortices. In addition, due to the mixing and convergence of the airflow in the downwash, vortices with larger intensity and size are generated. Due to the influence of the duct wall, the number of vortices generated near the rotor of the ducted rotor is small, and the airflow is not easy to converge in the downwash, so basically no vortices are generated. Usually vortices are the main source of noise. Therefore, the noise reduction duct of this embodiment effectively suppresses the generation and development of vortices, which can effectively reduce noise.

[0069] Figure 7The 1 / 3 octave frequency spectrum of a single isolated rotor and a ducted rotor is shown; X1 represents the sound pressure level curve for the isolated rotor, and X2 represents the sound pressure level curve for the ducted rotor. A comparative analysis shows that the overall trend of the sound pressure spectra for both rotors is similar, but at 1 BPF, the tonal noise level of the ducted rotor is significantly reduced, by approximately 7 dB. Furthermore, the sound pressure level of the ducted rotor is also significantly reduced within the wide frequency band from 3500 Hz to 10000 Hz, resulting in a 2.5 dB overall reduction in the sound pressure level. This demonstrates that the noise reduction duct of this embodiment effectively reduces the aerodynamic noise of the UAV rotor.

Claims

1. A noise reduction structure for a rotary wing UAV derived from a symmetrical airfoil, the rotary wing UAV comprising a fuselage (1), four connecting rods (3) fixedly connected in a "cross" shape in the circumferential direction of the fuselage (1), a motor base (5) fixedly provided at the distal end of each connecting rod, a motor (6) installed in the motor base (5), a rotor (7) fixedly installed at the upper end of the rotating shaft of the motor (6) by a clamping cap (9), and the rotor (7) driven by the motor (6) to rotate; the invention is characterized by: A noise reduction pipe (8) is fixedly arranged on the periphery of the rotor (7) and at a concentric position with the rotor (7); the pipe body (8a) of the noise reduction pipe (8) is an annular pipe with an inlet and an outlet passing therethrough, and the external shape of the pipe body (8a) includes an inlet lip shape, an inner cavity shape, and an outer edge shape; the inlet lip shape of the pipe body (8a) is semicircular; the inner cavity shape of the pipe body (8a) is a cylindrical cavity shape; and the outer edge shape of the pipe body (8a) is derived from a symmetrical airfoil.

2. The noise reduction structure of a rotary-wing UAV derived from a symmetrical airfoil according to claim 1, characterized in that: The noise reduction pipe (8) has three support arms (8b) uniformly distributed along the circumferential direction at the bottom of its pipe body (8a); one end of the support arm (8b) is fixedly connected to the pipe body (8a); the other end of the support arm (8b) is connected to a pipe base (8d); and the pipe base (8d) is a sleeve sleeved on the motor base (5).

3. The noise reduction structure of a rotary-wing UAV derived from a symmetrical airfoil according to claim 2, characterized in that: A slider and a slide groove are used to connect the support arm (8b) and the pipe base (8d), wherein the slider (8c) is fixedly connected to the end of the support arm (8b), and a slide groove is axially arranged at a corresponding position of the pipe base (8d), and the slider (8c) can be slidably assembled in the slide groove and axially locked.

4. The noise reduction structure of a rotary-wing UAV derived from a symmetrical airfoil according to claim 3, characterized in that: The axial locking is achieved by providing ratchets on the sides of the slider and the sliding groove, and utilizing the ratchets to perform axial locking.

5. The noise reduction structure of a rotary-wing UAV derived from a symmetrical airfoil according to claim 1, characterized in that: The outer edge shape of the tube body (8a) is formed by rotating the outer edge curve, and the axis of rotation is the central axis of the tube body (8a); the outer edge curve is formed by connecting a curved segment and a straight segment; Establish coordinate system A: the semicircular vertex of the inlet lip is the coordinate origin O, the axial direction from the tube inlet to the outlet is the positive direction of the x-axis, and the radial direction from the inner wall of the tube to the outer wall of the tube is the positive direction of the y-axis; The equation of the curve segment in coordinate system A is as follows: In formula (1): The y-axis coordinate of the curve segment is represented by y, and the value range of y is [-0.5d, 0.5d], where positive and negative represent the direction; d is the semicircular diameter of the inlet lip along the mid-axis section of the tube body; A, B, C, D, and E are constants obtained by fitting the airfoil based on ideal flow theory and wind tunnel test data; they are: A = 0.297, B = -0.126, C = -0.352, D = 0.284, E = -0.102; X is the normalized result of the airfoil chord length, and the value of X is represented by formula (2): In formula (2): The x-axis coordinate of the curve segment is represented by x, and the value range of x is [0.5d+0.3L,L]; L is the chord length, which is the axial height of the tube body. The chord length L is represented by formula (3): In formula (3): R1 is the inner radius of the tube body, and the inner radius of each part is consistent; One end of the straight line segment is connected to the semicircular portion of the inlet lip, and the other end is connected to the curved line segment. The length of the straight line segment is L1, where L1 = 0.3L.

6. The noise reduction structure of a rotary-wing UAV derived from a symmetrical airfoil according to claim 5, characterized in that: Will The values ​​are: The tip clearance S is taken as The tip clearance S refers to the gap between the rotor tip and the inner cavity wall of the tube body.

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