A ducted UAV noise reduction device based on blade tip acoustic metamaterial

Abstract

The present invention discloses a ducted UAV noise reduction device based on blade tip acoustic metamaterial, comprising: a UAV body, the UAV body comprising a duct, a first propeller and a second propeller, the first propeller and the second propeller being coaxial and arranged inside the duct at intervals along the axial direction of the duct; a noise reduction unit, mounted on the inner side wall of the duct, the interior of the noise reduction unit being a curved channel of equal cross-section, the channel being connected to the flow channel formed by the duct; wherein the channel can generate secondary noise under the excitation of the approximately periodic pressure pulsation generated by the rotating first propeller and the second propeller, the amplitude of the secondary noise at the blade frequency or its harmonic frequency is close to the amplitude of the blade frequency or its harmonic noise of the UAV body, and the phase is close to anti-phase and cancels each other, thereby reducing the blade frequency or its harmonic noise of the UAV body. The present invention has the advantages of simple structure, low cost, and no influence on the efficiency of the UAV.

Description

Technical Field

[0001] The present invention relates to the technical field of unmanned aerial vehicles, and in particular to a ducted unmanned aerial vehicle noise reduction device based on blade tip acoustic metamaterials. Background Art

[0002] A drone is an unmanned aircraft controlled by a radio remote control device and a self-contained program control device. It has the advantages of small size, low cost, easy use, low environmental requirements, and strong survivability, so it is widely used in military and civilian fields. However, the noise problem during drone flight has restricted its development so far. The noise reduction technology of drones can be divided into active noise reduction and passive noise reduction. Many of the patents for drone noise reduction that have been published use active noise reduction technology, but active noise reduction occupies a large space, has a high cost and poor reliability. Passive noise reduction technology includes control from the propagation path, such as installing a sound insulation structure outside the motor to reduce motor noise, installing sound-absorbing materials on the drone to reduce high-frequency noise, etc., as well as control from reducing the intensity of the noise source. Control from the propagation path usually requires a longer duct or structure for installing a sound-absorbing structure to achieve a better noise reduction effect. Therefore, many scholars have tried to control fan noise from the perspective of reducing the intensity of drone noise sources, such as the drone propeller noise reduction design based on acoustic black holes, noise reduction propellers based on bionic design (the leading edge of the blade adopts a sinusoidal nodule structure, the trailing edge adopts an isosceles triangle serrated structure, and the suction surface is bonded with a microarray diaphragm structure), and noise reduction by tilting and sweeping the stator. However, these passive noise reduction solutions usually affect the noise reduction performance of drones.

[0003] In terms of using resonators to reduce the single-tone noise of rotating machinery, Neise and Koopmann installed a 1 / 4 wavelength tube at the volute tongue of the centrifugal fan, and used the 1 / 4 wavelength tube to generate secondary noise with approximately equal amplitude and approximately opposite phase to offset the blade frequency noise of the fan. Then Gorny et al. extended this secondary noise cancellation method to the control of reducing the blade frequency noise and harmonic noise of the axial flow fan. Koopmann et al. used the secondary noise with dipole characteristics generated by two resonators installed at a close distance in the area where the fan blades pass to simultaneously reduce the noise outside the fan inlet and outlet. Grissom et al. installed a resonator at the tip of the unducted propeller to change the sound field of the propeller system at the blade passing frequency and its harmonic frequency. However, these resonators take up a lot of space and are not suitable for practical engineering applications. Summary of the invention

[0004] Based on this, it is necessary to provide a ducted UAV noise reduction device based on blade tip acoustic metamaterials to address the above technical problems.

[0005] A ducted UAV noise reduction device based on blade tip acoustic metamaterials, comprising:

[0006] A drone body, the drone body comprising a duct, a first propeller and a second propeller, wherein the first propeller and the second propeller are coaxial and arranged inside the duct at intervals along the axis direction of the duct;

[0007] A noise reduction unit is installed on the inner wall of the duct, the interior of the noise reduction unit is a curved channel with a constant cross-section, and the channel is connected to the flow channel formed by the duct;

[0008] Among them, the channel can generate secondary noise under the excitation of the approximately periodic pressure pulsation generated by the rotating first propeller and the second propeller. The amplitude of the secondary noise at the blade frequency or its harmonic frequency is close to the amplitude of the blade frequency or its harmonic noise of the drone body and the phase is close to anti-phase, so they cancel each other out, thereby reducing the blade frequency or its harmonic noise of the drone body.

[0009] In one embodiment, the noise reduction unit comprises:

[0010] A first labyrinth-type acoustic metamaterial, wherein the first labyrinth-type acoustic metamaterial is mounted on an inner side wall of a first propeller blade tip duct, and an inner channel of the first labyrinth-type acoustic metamaterial is connected to a flow channel formed by the duct;

[0011] A second labyrinth-type acoustic metamaterial is installed on the inner side wall of the second propeller blade tip duct, and an internal channel of the second labyrinth-type acoustic metamaterial is connected to a flow channel formed by the duct.

[0012] In one embodiment, the cross-sections of the first labyrinth type acoustic metamaterial and the second labyrinth type acoustic metamaterial are rectangular, circular or polygonal, and the center lines of the first labyrinth type acoustic metamaterial and the second labyrinth type acoustic metamaterial are plane curves or space curves. The number of the first labyrinth type acoustic metamaterial and the second labyrinth type acoustic metamaterial is at least one, and the plurality of the first labyrinth type acoustic metamaterials and the second labyrinth type acoustic metamaterials are respectively arranged on the same circumference of the blade tip duct wall.

[0013] In one embodiment, the drone body further includes:

[0014] A lip, disposed at the entrance of the drone body and connected to the duct;

[0015] a first support frame, fixed to an upper portion of an inner wall of the duct, a first motor being mounted on the first support frame, and the first motor being connected to the first propeller;

[0016] a second support frame, fixed to the lower part of the inner wall of the duct, a second motor is mounted on the second support frame, and the second motor is connected to the second propeller;

[0017] The skirt is arranged at the outlet of the drone body and connected to the duct, and a spoiler is arranged on the inner side of the skirt.

[0018] The above-mentioned ducted UAV noise reduction device based on blade tip acoustic metamaterial, by arranging a noise reduction unit on the inner wall of the duct, the noise reduction unit can generate secondary noise under the excitation of the approximately periodic pressure pulsation generated by the rotating first propeller and the second propeller. The amplitude of the secondary noise at the blade frequency or its harmonic frequency is close to the phase opposite to the amplitude of the original UAV blade frequency or its harmonic noise, and they cancel each other out, thereby reducing the blade frequency or harmonic noise of the UAV body. It has the advantages of simple structure, low cost, and no effect on the efficiency of the UAV. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 is a schematic diagram of the structure of the ducted UAV of the present invention;

[0021] Figure 2 is a cross-sectional view of a ducted UAV of the present invention;

[0022] Figure 3 is a cross-sectional view of a ducted UAV noise reduction device based on blade tip acoustic metamaterials of the present invention;

[0023] Figure 4 is a structural schematic diagram of a first noise reduction unit of the present invention;

[0024] Figure 5 is a front view of a first noise reduction unit of the present invention;

[0025] Figure 6 yes Figure 5 Schematic cross-sectional view along line AA;

[0026] Figure 7 is a structural schematic diagram of a second noise reduction unit of the present invention;

[0027] Figure 8 is a front view of a second noise reduction unit of the present invention;

[0028] Fig. 9 yes Figure 8 Schematic cross-sectional view along line BB;

[0029] Fig.10 yes Figure 8 Schematic cross-sectional view along line CC;

[0030] Fig.11 is a schematic structural diagram of a third noise reduction unit of the present invention;

[0031] Fig.12 is a front view of a third noise reduction unit of the present invention;

[0032] Fig.13 yes Fig.12 Schematic cross-sectional view along line DD;

[0033] Fig.14 yes Fig.12 Schematic cross-sectional view along line EE;

[0034] Fig.15 is a structural schematic diagram of a fourth noise reduction unit of the present invention;

[0035] Fig.16 yes Fig.15 Schematic cross-sectional view along line FF.

[0036] Fig.17 It is a schematic diagram of the structure of the straight branch pipe of the present invention;

[0037] Fig.18 It is a cross-sectional view of the straight branch pipe of the present invention. DETAILED DESCRIPTION

[0038] In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. Preferred embodiments of the present invention are provided in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0039] It should be noted that when an element is referred to as being "fixed to" another element, it may be directly on the other element or there may be an intermediate element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be an intermediate element at the same time.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0041] See also Figure 1-16 As shown, an embodiment of the present invention provides a ducted UAV noise reduction device based on blade tip acoustic metamaterial, comprising:

[0042] A drone body 1, the drone body 1 comprising a duct 2, a first propeller 3 and a second propeller 4, the first propeller 3 and the second propeller 4 being coaxial and spaced apart inside the duct 2 along the axis direction of the duct 2;

[0043] A noise reduction unit 5 is installed on the inner wall of the duct 2. The interior of the noise reduction unit 5 is a curved channel 53 with a constant cross section. The channel 53 is connected to the flow channel formed by the duct 2.

[0044] Among them, the channel 53 can generate secondary noise under the excitation of the approximately periodic pressure pulsation generated by the rotating first propeller 3 and the second propeller 4. The amplitude of the secondary noise at the blade frequency or its harmonic frequency is close to the amplitude of the blade frequency or its harmonic noise of the drone body and the phase is close to the opposite phase, so they cancel each other out, thereby reducing the blade frequency or its harmonic noise of the drone body.

[0045] The above-mentioned ducted UAV noise reduction device based on blade tip acoustic metamaterial, by arranging a noise reduction unit 5 on the inner wall of the duct 2, uses the channel 51 of the noise reduction unit 5 to generate secondary noise, the amplitude of the secondary noise at the blade frequency or its harmonic frequency is close to the phase opposite to the amplitude of the original UAV blade frequency or its harmonic noise, and cancels each other out, thereby reducing the blade frequency or harmonic noise of the UAV body 1, and has the advantages of simple structure, low cost, and no influence on the efficiency of the UAV, etc.

[0046] In one embodiment of the present invention, the noise reduction unit 5 includes:

[0047] A first labyrinth-type acoustic metamaterial 51, wherein the first labyrinth-type acoustic metamaterial 51 is installed on the inner side wall of the blade tip duct of the first propeller 3, and the inner curved channel of the first labyrinth-type acoustic metamaterial 51 is connected to the flow channel formed by the duct 2;

[0048] The second labyrinth type acoustic metamaterial 52 is installed on the inner wall of the blade tip duct of the second propeller 4 , and the inner curved channel of the second labyrinth type acoustic metamaterial 52 is connected to the flow channel formed by the duct 2 .

[0049] In this embodiment, under the excitation of the approximately periodic pressure pulsation generated by the rotating first propeller 3 and the second propeller 4, the internal curved channels of the first labyrinth type acoustic metamaterial 51 and the internal curved channels of the second labyrinth type acoustic metamaterial 52 will generate secondary noise. By making the amplitude of the secondary noise at the blade frequency or its harmonic frequency close to the phase opposite to the amplitude of the original UAV blade frequency or its harmonic noise, the blade frequency or harmonic noise of the UAV body 1 can be reduced.

[0050] In one embodiment of the present invention, the cross-sections of the first labyrinth type acoustic metamaterial 51 and the second labyrinth type acoustic metamaterial 52 may be rectangular, circular or polygonal, etc., and the center lines of the first labyrinth type acoustic metamaterial 51 and the second labyrinth type acoustic metamaterial 52 may be plane curves or space curves. In addition, the number of the first labyrinth type acoustic metamaterial and the second labyrinth type acoustic metamaterial may be one or more, and the plurality of the first labyrinth type acoustic metamaterials and the second labyrinth type acoustic metamaterials are respectively arranged on the same circumference of the blade tip duct wall.

[0051] See also Figure 4-16 The present invention provides four equivalent acoustic metamaterial structures with the same acoustic properties as the straight branch pipe. It can be seen that compared with the straight branch pipe, the maze-type equivalent acoustic metamaterial occupies significantly less space in the direction perpendicular to the duct 2, and is more suitable for engineering applications.

[0052] It should be noted that the present invention first obtains the parameters of the straight side branch pipe that can reduce the blade frequency or its harmonic noise of the UAV by adjusting the depth, cross-sectional size (or opening perforation rate), number and installation position (including axial position and circumferential position) of the straight side branch pipe, and then, according to the actual installation conditions and with the help of finite element tools, an equivalent acoustic metamaterial with the same acoustic properties as the straight side branch pipe is designed to replace the side branch pipe to reduce the UAV noise.

[0053] See also Figure 17-18 As shown, a straight bypass pipe 6 is provided on the inner wall of the duct 2, and the straight bypass pipe 6 includes a first straight bypass pipe 62 and a second straight bypass pipe 63, wherein the first straight bypass pipe 62 and the second straight bypass pipe 63 are respectively installed on the duct wall surfaces of the blade tops of the second propeller 4 and the first propeller 3.

[0054] Among them, the first straight bypass pipe 62 and the second straight bypass pipe 63 both include a first sleeve 621 and a first piston 622, one end of the first sleeve 621 is connected to the flow channel formed by the duct 2, the other end of the first sleeve 621 is penetrated to the outside of the duct 2 along the radial direction of the duct 2, and one end of the first piston 622 is movably penetrated inside the other end of the first sleeve 621; the first sleeve 621 forms a depth-adjustable channel 61 through the first piston 622.

[0055] In this embodiment, under the premise of keeping the rotation speed of the propellers (the first propeller 3 and the second propeller 4) of the drone unchanged, by adjusting the depth of the channel 61, the proximity of its acoustic modal frequency to the blade frequency or its harmonic frequency can be changed, thereby changing the amplitude and phase of the secondary noise generated by the first straight bypass 62 and the second straight bypass 63 at the blade frequency or its harmonic frequency.

[0056] When the same pressure excitation is applied to the openings of the first straight bypass pipe 62 and the second straight bypass pipe 63, the larger the cross-sectional size, the greater the noise generated. Therefore, by using straight bypass pipes with different cross-sectional sizes, secondary noises of different amplitudes can be obtained. Considering that the amplitude and phase of the pressure pulsation on the wall of the duct 2 in the blade passing area change significantly along the axial direction, the amplitude and phase of the secondary noise generated by it can also be changed by adjusting the axial installation position of the straight bypass pipe 6 on the duct 2. For the blade frequency or its harmonic noise that contributes a large amount to the rotation-static interference, the amplitude and phase of the pressure pulsation on the wall of the duct 2 in the blade area will also change along the circumferential direction. Therefore, the amplitude and phase of the secondary noise generated by it can also be changed by adjusting the circumferential installation position of the straight bypass pipe 6 on the duct 2. In addition, installing different numbers of straight bypass pipes in the circumferential direction (for example, 2 each of the first straight bypass pipe 62 and the second straight bypass pipe 63) can also obtain secondary noises of different amplitudes.

[0057] In summary, by adjusting the depth, cross-sectional dimensions (or opening perforation ratio), number and axial and circumferential installation positions of the straight branch pipes (the first straight branch pipe 62 and the second straight branch pipe 63) in the duct 2, the amplitude and phase of the secondary noise can be changed. When the amplitude of the secondary noise at the blade frequency or its harmonic frequency is close to the amplitude of the original UAV noise, and the phase is close to anti-phase, the blade frequency or its harmonic noise of the UAV will be reduced. In this way, the parameters of the straight branch pipe that can reduce the blade frequency or its harmonic noise of the UAV can be obtained. Then, according to the actual installation conditions and with the help of finite element tools, an equivalent acoustic metamaterial with the same acoustic properties as the straight branch pipe is designed to replace the branch pipe to reduce the UAV noise.

[0058] In one embodiment of the present invention, the drone body 1 further includes:

[0059] A lip 11 is provided at the entrance of the drone body 1 and connected to the duct 2;

[0060] A first support frame 12 is fixed to the upper part of the inner wall of the inner channel 21. A first motor 15 is installed on the first support frame 12. The first motor 15 is connected to the first propeller 3. The first motor 15 can drive the first propeller 3 to rotate.

[0061] A second support frame 13 is fixed to the lower part of the inner wall of the inner channel 21. A second motor 16 is installed on the second support frame 13. The second motor 16 is connected to the second propeller 4. The second motor 16 can drive the second propeller 4 to rotate.

[0062] The skirt 14 is arranged at the outlet of the drone body 1 and connected to the duct 2 , and a spoiler 17 is arranged on the inner side of the skirt 14 .

[0063] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0064] The above-described embodiments only express several implementation methods of the present invention, but they cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims.

Claims

1. A ducted UAV noise reduction device based on blade tip acoustic metamaterial, characterized in that: include: A drone body, the drone body comprising a duct, a first propeller and a second propeller, wherein the first propeller and the second propeller are coaxial and arranged inside the duct at intervals along the axis direction of the duct; A noise reduction unit is installed on the inner wall of the duct, the interior of the noise reduction unit is a curved channel with a constant cross-section, and the channel is connected to the flow channel formed by the duct; Wherein, the channel can generate secondary noise under the excitation of the approximately periodic pressure pulsation generated by the rotating first propeller and the second propeller, and the amplitude of the secondary noise at the blade frequency or its harmonic frequency is close to the amplitude of the blade frequency or its harmonic noise of the drone body and the phase is close to anti-phase, so they cancel each other out, thereby reducing the blade frequency or its harmonic noise of the drone body; The noise reduction unit comprises: A first labyrinth-type acoustic metamaterial, wherein the first labyrinth-type acoustic metamaterial is mounted on an inner side wall of a first propeller blade tip duct, and an inner channel of the first labyrinth-type acoustic metamaterial is connected to a flow channel formed by the duct; A second labyrinth-type acoustic metamaterial is installed on the inner side wall of the second propeller blade tip duct, and an internal channel of the second labyrinth-type acoustic metamaterial is connected to a flow channel formed by the duct.

2. The ducted UAV noise reduction device based on blade tip acoustic metamaterial according to claim 1, characterized in that: The cross-sections of the first labyrinth type acoustic metamaterial and the second labyrinth type acoustic metamaterial are rectangular, circular or polygonal, and the center lines of the first labyrinth type acoustic metamaterial and the second labyrinth type acoustic metamaterial are plane curves or space curves. The number of the first labyrinth type acoustic metamaterial and the second labyrinth type acoustic metamaterial is at least one, and the plurality of the first labyrinth type acoustic metamaterials and the second labyrinth type acoustic metamaterials are respectively arranged on the same circumference of the blade tip duct wall.

3. The ducted UAV noise reduction device based on blade tip acoustic metamaterial according to claim 2, characterized in that: The drone body also includes: A lip, disposed at the entrance of the drone body and connected to the duct; a first support frame, fixed to an upper portion of an inner wall of the duct, a first motor being mounted on the first support frame, and the first motor being connected to the first propeller; a second support frame, fixed to the lower part of the inner wall of the duct, a second motor is mounted on the second support frame, and the second motor is connected to the second propeller; The skirt is arranged at the outlet of the drone body and connected to the duct, and a spoiler is arranged on the inner side of the skirt.

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