Differential pressure driven propeller micro-nano air curtain noise reduction system and noise reduction method thereof

Abstract

The differential pressure driven propeller micro-nano air curtain noise reduction system comprises a gas-liquid mixing cavity and a high-speed stirrer, and the gas-liquid mixing cavity is arranged in the internal space of the tail of an aircraft; the high-speed stirrer is arranged in the gas-liquid mixing cavity; the gas-liquid mixing cavity is provided with a gas inlet, a water inlet and a micro-nano bubble outlet, the diameter of the water inlet is D1, and the diameter of the micro-nano bubble outlet is D2; the included angle between the tangent line of the molded line at the micro-nano bubble outlet and the central axis of the aircraft is alpha, and the angle between the micro-nano bubble outlet and the central axis of the aircraft is-alpha; the center-to-center distance between the water inlet and the micro-nano bubble outlet is D3, and D3 is larger than 6 * D1 and larger than 3 * D2; when the spraying speed V3 of the micro-nano bubbles is equal to V / cos alpha, the micro-nano bubbles enter a potential flow area and spread downstream along the streamline of the aircraft, and a micro-nano air curtain is formed and wraps the periphery of the propeller. A micro-nano air curtain is formed around the propeller, acoustic impedance is increased to cause acoustic wave transmission loss, and the radiation noise of the propeller is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of stealth of vehicles and ships, in particular to a propeller micro-nano air curtain noise reduction system driven by differential pressure and a noise reduction method thereof. Background Art

[0002] The noise of the propeller of an underwater vehicle or a large surface ship is the main source of its radiated noise, which seriously affects the quietness and comfort of the ship. At present, some effects have been achieved in the existing noise reduction technologies, but there are obvious deficiencies or defects, which are mainly reflected in:

[0003] Propeller structure design: Through the propeller structure design, the cavitation initiation of the propeller blade can be effectively suppressed, but tip vortex cavitation is an unavoidable cavitation form that will eventually occur as the ship speed increases; and the radiated noise in the cavitation state of the propeller is generally about 20 dB higher than that in the non-cavitation state, which is a significant source of radiated noise for underwater vehicles and large surface ships. In addition, the propeller structure design for the purpose of noise reduction often sacrifices the propulsion efficiency and has a high manufacturing cost.

[0004] Increasing the propeller sound barrier: A physical barrier is set around the propeller to block the propagation of the propeller noise. The most commonly used one is the ducted propeller, that is, a duct is installed outside the traditional propeller, and the duct is fixed to the tail of the underwater vehicle or the large surface ship through a front stator or a rear stator. This method increases the acoustic impedance in the sound propagation path and achieves a certain noise reduction effect. However, due to the interaction between the tip of the propeller blade and the boundary layer flow of the inner wall of the duct, a tip clearance flow is formed, and the flow mechanism is extremely complex, including tip leakage vortices, tip separation vortices and the induced secondary vortices. There is a complex interaction mechanism between the vortex systems. Research shows that the cavitation initiation of the tip clearance vortex appears at the tip clearance leading edge separation vortex, and there is a significant increase in the radiated noise caused by cavitation of about 20 dB, and there is a high risk of cavitation erosion on both the tip of the rotor and the inner wall of the duct. In addition, due to the appearance of the duct, the navigation resistance is increased and the propulsion efficiency is reduced.

[0005] Propeller and Tail Acoustic Absorbing Material Application: Acoustic absorbing materials usually adopt resonance acoustic absorption structures or gradient transition layer structures. Generally, fillers containing a large number of air bubbles are mixed into the materials or metal microbeads are added, etc., to increase the acoustic impedance of the materials, enabling sound waves to enter the acoustic absorbing materials without reflection and causing most of the incident sound waves to be absorbed. Using acoustic absorbing materials in the propeller and tail can, to a certain extent, block the propagation of propeller noise. However, as a prominent component suspended at the tail of an underwater vehicle or below the waterline of a large surface ship, the propeller has a wide range of noise propagation paths. The sound energy propagated through the propeller itself or the main body tail is only a very small part of it, and most of it is radiated from around the propeller. Therefore, using acoustic absorbing materials in the propeller and tail cannot fundamentally form a protection against propeller noise. In addition, general acoustic absorbing materials are composed of multi-component materials and have a short lifespan, requiring regular maintenance and replacement, which increases the operating cost.

[0006] Therefore, the existing propeller noise reduction technologies currently have deficiencies such as low propulsion efficiency, increased cavitation risk, and obvious protection loopholes.

[0007] For this reason, we propose a differential pressure-driven propeller micro-nano air curtain noise reduction system and its noise reduction method. Summary of the Invention

[0008] The applicant of the present invention aims at the above-mentioned shortcomings in the existing production technologies, and provides a differential pressure-driven propeller micro-nano air curtain noise reduction system and its noise reduction method, thereby forming a micro-nano air curtain around the propeller, increasing the acoustic impedance and causing sound wave transmission loss, and achieving a reduction in the radiated noise of the propeller.

[0009] The technical solution adopted by the present invention is as follows:

[0010] A differential pressure-driven propeller micro-nano air curtain noise reduction system includes:

[0011] A gas-liquid mixing chamber, which is arranged in the internal space at the tail of the vehicle;

[0012] A high-speed stirrer, which is arranged in the gas-liquid mixing chamber and is used to generate micro-nano bubbles;

[0013] A gas inlet, which is arranged on the gas-liquid mixing chamber and is communicated with a gas source;

[0014] A water inlet, which is arranged on the gas-liquid mixing chamber and has a diameter of D1;

[0015] A micro-nano bubble outlet, which is arranged on the gas-liquid mixing chamber and is used to eject micro-nano bubbles. It has a diameter of D2. The tangent of the profile line at the micro-nano bubble outlet forms an angle α with the central axis of the vehicle, and the angle between the micro-nano bubble outlet and the central axis of the vehicle is -α;

[0016] Among them, a propeller is externally provided at the tail of the vehicle; the central distance between the water inlet and the micro-nano bubble outlet is D3, and 6×D1>D3>3×D2;

[0017] When the ejection speed V3 of the micro-nano bubbles is V / cosα, the micro-nano bubbles enter the potential flow region, and the micro-nano bubbles propagate downstream along the streamline of the vehicle, forming a micro-nano air curtain wrapped around the propeller.

[0018] Its further features are as follows:

[0019] The micro-nano bubbles are micron-level and nano-level bubbles.

[0020] The vehicle is an underwater vehicle, and the gas source is a liquid nitrogen storage tank, which is connected to the gas inlet.

[0021] The liquid nitrogen storage tank is arranged inside the underwater vehicle, and an airtight piston is arranged in the liquid nitrogen storage tank, and the airtight piston is driven to move through a driving mechanism.

[0022] The vehicle is a large surface ship, and the gas inlet is arranged above the waterline of the large surface ship, and air is used as the gas source.

[0023] The angle α between the micro-nano bubble outlet and the central axis of the vehicle ranges from 10° to 45°.

[0024] The micro-nano air curtain is annular.

[0025] The micro-nano air curtain is fan-shaped.

[0026] One-way valves capable of flowing into the gas-liquid mixing chamber are provided at both the gas inlet and the water inlet, and a one-way valve capable of flowing out of the vehicle is provided at the micro-nano bubble outlet.

[0027] This application also provides a method for reducing noise of a propeller micro-nano air curtain driven by pressure difference, including the following steps:

[0028] Start the propeller, and the forward speed of the vehicle is V;

[0029] Start the high-speed stirrer. The gas enters the gas-liquid mixing chamber through the gas inlet, and the liquid enters the gas-liquid mixing chamber through the water inlet to form a gas-liquid mixed fluid; the gas-liquid mixed fluid rotates at high speed under the action of pressure, and a negative pressure axis is formed in the middle of the gas-liquid mixing chamber, and high-speed and strong shear and high-frequency pressure pulsation are generated at the gas-liquid contact interface to form an artificial extreme condition. Under this condition, a large number of micron-level and nano-level bubbles are generated, which are collectively called micro-nano bubbles;

[0030] As the high-speed stirrer rotates, the gas and liquid in the gas-liquid mixing chamber gradually increase. When the pressure inside the gas-liquid mixing chamber is higher than the external pressure, the micro-nano bubbles rotating at high speed are ejected from the micro-nano bubble outlet under the drive of the pressure difference. The ejection speed of the micro-nano bubbles from the micro-nano bubble outlet is V3;

[0031] By adjusting the power of the high-speed stirrer, the ejection speed V3 of the micro-nano bubbles is adjusted so that V3 = V / cosα, enabling the micro-nano bubbles to have a high enough speed to break through the turbulent boundary layer and enter the potential flow region outside the circumferential boundary layer;

[0032] The micro-nano bubbles propagate downstream along the streamline of the vehicle. The dissolution rate of the micro-nano bubbles in water exceeds 85%, and they remain in the water in the form of bubbles for a long time, forming a micro-nano air curtain that wraps around the propeller;

[0033] The radiated noise of the propeller passes through the micro-nano air curtain, and the acoustic wave transmission loss caused by impedance can reduce the far-field radiated noise of the propeller and improve the acoustic performance of the vehicle.

[0034] The beneficial effects of the present invention are as follows:

[0035] The structure of the present invention is compact and reasonable, and it is convenient to operate. Through the propeller micro-nano air curtain noise reduction system driven by pressure difference, by adjusting the power of the high-speed stirrer, the ejection speed V3 of the micro-nano bubbles is adjusted. When V3 = V / cosα, the micro-nano bubbles have a high enough speed to break through the turbulent boundary layer and enter the potential flow region outside the circumferential boundary layer. The micro-nano bubbles propagate downstream along the streamline of the vehicle. The dissolution rate of the micro-nano bubbles in water can exceed 85%, and they remain in the water in the form of bubbles for a long time, forming a micro-nano air curtain. The micro-nano air curtain is annular and wraps around the propeller, causing acoustic wave transmission loss of the propeller radiated noise and achieving the effect of reducing the propeller radiated noise.

[0036] Meanwhile, the present invention also has the following advantages:

[0037] (1) It has a simple structure, is easy to implement, has a significant noise reduction effect, and does not reduce the propulsion efficiency.

[0038] (2) The diameter of the water inlet is D1, the diameter of the micro-nano bubble outlet is D2, and the center distance between the water inlet and the micro-nano bubble outlet is D3. Among them, it is required that 6×D1 > D3 > 3×D2; to ensure that the water flow entering the gas-liquid mixing chamber from the water inlet does not interfere with the micro-nano bubbles ejected from the micro-nano bubble outlet, and the turbulent boundary layer reattached at the micro-nano bubble outlet is still very thin, facilitating the micro-nano bubbles to break through the confinement of the turbulent boundary layer and enter the potential flow region.

[0039] (3) By utilizing the negative pressure axis generated by a high-speed stirrer, the gas and seawater are fully mixed. Under the formed artificial extreme conditions, a large number of micron-sized and nanometer-sized bubbles are continuously generated. The dissolution rate of micro-nano bubbles in water exceeds 85%, and they remain in the water in the form of bubbles for a long time, which is the key to the long-term and stable existence of the gas curtain around the propeller. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a schematic diagram of the implementation process of the underwater vehicle of the present invention.

[0041] Figure 2 It is a schematic cross-sectional view of the underwater vehicle of the present invention after assembling the noise reduction system.

[0042] Figure 3 is Figure 2 a partially enlarged schematic diagram in

[0043] Figure 4 is Figure 3 a schematic diagram of the tail of the underwater vehicle in

[0044] Figure 5 It is a schematic diagram of the implementation process of the large surface ship of the present invention.

[0045] Figure 6 It is a schematic cross-sectional view of the large surface ship of the present invention after assembling the noise reduction system.

[0046] Figure 7 is Figure 6 a partially enlarged schematic diagram in

[0047] Figure 8 is Figure 7 a schematic diagram of the tail of the large surface ship in

[0048] Figure 9 It is a schematic diagram of the acoustic wave transmission loss caused by the micro-nano gas curtain impedance of the present invention.

[0049] Wherein: 1, vehicle; 2, propeller; 3, liquid nitrogen storage tank; 4, drive mechanism; 5, airtight piston; 6, gas inlet; 7, water inlet; 8, gas-liquid mixing chamber; 9, high-speed stirrer; 10, micro-nano bubble outlet; 11, streamline; 12, micro-nano gas curtain; 13, central axis; 14, water line. DETAILED DESCRIPTION OF THE INVENTION

[0050] The following will describe the detailed implementation of the present invention with reference to the accompanying drawings.

[0051] As Figures 1-9As shown in the figure, a differential pressure-driven propeller micro-nano air curtain noise reduction system includes a gas-liquid mixing chamber 8 and a high-speed stirrer 9. The gas-liquid mixing chamber 8 is provided with a gas inlet 6, a water inlet 7, and a micro-nano bubble outlet 10. The gas-liquid mixing chamber 8 is installed in the internal space at the tail of the vehicle 1. A propeller 2 is provided in the external space at the tail of the vehicle 1.

[0052] In one embodiment, both the gas inlet 6 and the water inlet 7 are provided with one-way valves that can flow into the gas-liquid mixing chamber 8, and the micro-nano bubble outlet 10 is provided with a one-way valve that can flow to the outside of the vehicle 1.

[0053] The high-speed stirrer 9 is arranged in the gas-liquid mixing chamber 8. The gas-liquid mixing chamber 8 is arranged in the internal space at the tail of the vehicle 1. The gas inlet 6 is communicated with a gas source, and gas supply is carried out through the gas source.

[0054] The water inlet 7 and the micro-nano bubble outlet 10 are grooved and installed flatly on the surface of the vehicle 1.

[0055] The pressure inside the gas-liquid mixing chamber 8 is P1, and the pressure outside the underwater vehicle is P2.

[0056] The diameter of the water inlet 7 is D1, the diameter of the micro-nano bubble outlet 10 is D2, and the center distance between the water inlet 7 and the micro-nano bubble outlet 10 is D3. Among them, it is required that 6×D1>D3>3×D2; to ensure that the water flow entering the gas-liquid mixing chamber 8 from the water inlet 7 does not interfere with the micro-nano bubbles ejected from the micro-nano bubble outlet 10, and the reattached turbulent boundary layer at the micro-nano bubble outlet 10 is still very thin, facilitating the micro-nano bubbles to break out of the bondage of the turbulent boundary layer and enter the potential flow area.

[0057] The included angle between the tangent of the profile line at the micro-nano bubble outlet 10 and the central axis 13 is α, and the angle between the micro-nano bubble outlet 10 and the central axis 13 of the vehicle 1 is -α, so that the direction of the ejected micro-nano bubbles and the central axis 13 of the underwater vehicle is also -α, 45°≥α≥10°, that is, the direction of the ejected micro-nano bubbles is symmetric with the tangent of the profile line at the micro-nano bubble outlet 10.

[0058] Start the propeller 2, and the propeller 2 drives the vehicle 1 to travel. The speed of the vehicle is V.

[0059] Turn on the high-speed stirrer 9, a low-pressure area is formed in the gas-liquid mixing chamber 8. The gas in the gas source enters the gas-liquid mixing chamber 8 through the gas inlet 6, and the external liquid enters the gas-liquid mixing chamber 8 through the water inlet 7. The gas and the liquid are fully mixed in the gas-liquid mixing chamber 8 to form a gas-liquid mixed fluid. The gas-liquid mixed fluid rotates at a high speed under the action of pressure and forms a negative pressure axis in the middle of the gas-liquid mixing chamber 8, generating high-speed and powerful shear and high-frequency pressure pulsations at the gas-liquid contact interface, creating an artificial extreme condition. Under this condition, a large number of micro-scale and nano-scale bubbles are generated, collectively referred to as micro-nano bubbles. The speed of the gas entering the gas-liquid mixing chamber 8 from the gas inlet 6 is V1, and the speed of the liquid entering the gas-liquid mixing chamber 8 from the water inlet 7 is V2.

[0060] As the high-speed stirrer 9 operates, the gas and liquid in the gas-liquid mixing chamber 8 gradually increase. When the pressure inside the gas-liquid mixing chamber 8 is higher than the external pressure, the high-speed rotating micro-nano bubbles are ejected from the micro-nano bubble outlet 10 under the drive of the pressure difference. The speed of the micro-nano bubbles ejected from the micro-nano bubble outlet 10 is V3.

[0061] Adjust the ejection speed V3 of the micro-nano bubbles by adjusting the power of the high-speed stirrer 9. When V3 = V / cosα, the micro-nano bubbles have a high enough speed to break through the turbulent boundary layer and enter the potential flow region outside the wake boundary layer. The micro-nano bubbles propagate downstream along the streamline 11 of the vehicle 1. The dissolution rate of the micro-nano bubbles in water can exceed 85%, and they remain in the water in the form of bubbles for a long time, forming a micro-nano gas curtain 12. The micro-nano gas curtain 12 wraps around the propeller 2.

[0062] As Figure 9 shown, the radiated noise of the propeller 2 passes through the micro-nano gas curtain 12. Due to the acoustic wave transmission loss caused by impedance, in the frequency band of 100 Hz to 10 kHz, a sound insulation amount of up to 30 dB can be achieved, which plays a role in reducing the far-field radiated noise of the propeller 2, avoiding the detection and attack of underwater equipment such as sonar and torpedoes, and improving the stealth performance of the underwater vehicle.

[0063] In one embodiment, the vehicle 1 is an underwater vehicle, and the central axis of the underwater vehicle is the central axis 13.

[0064] Furthermore, the axis of the propeller 2 and the axis of the high-speed stirrer 9 both coincide with the central axis 13 of the underwater vehicle.

[0065] Furthermore, the gas inlet 6 is arranged inside the underwater vehicle. The gas source is a liquid nitrogen storage tank 3. The liquid nitrogen storage tank 3 is arranged inside the underwater vehicle. An airtight piston 5 is arranged in the liquid nitrogen storage tank 3, and the airtight piston 5 is driven to move by a driving mechanism 4. The driving mechanism 4 can be a motor, a push rod, etc. The driving mechanism 4 is arranged inside the underwater vehicle. The liquid nitrogen storage tank 3 is communicated with the gas inlet 6.

[0066] Further, start the propeller 2 to drive the underwater vehicle to move. Drive the airtight piston 5 to move upward through the drive mechanism 4, and then squeeze the liquid nitrogen in the liquid nitrogen storage tank 3 into the gas inlet 6 to turn it into nitrogen gas. Start the high-speed stirrer 9. The high-speed stirrer 9 forms a low-pressure area in the gas-liquid mixing chamber 8. The gas enters the gas-liquid mixing chamber 8 through the gas inlet 6, and the liquid enters the gas-liquid mixing chamber 8 through the water inlet 7. The gas and the liquid are fully mixed in the gas-liquid mixing chamber 8 to form a gas-liquid mixed fluid. The gas-liquid mixed fluid rotates at high speed under the action of pressure, and a negative pressure axis is formed in the middle of the gas-liquid mixing chamber 8. High-speed and strong shearing and high-frequency pressure pulsations are generated at the gas-liquid contact interface to form an artificial extreme condition. Under this condition, a large number of micron-sized and nano-sized bubbles are generated, collectively referred to as micro-nano bubbles.

[0067] Further, the gas and liquid in the gas-liquid mixing chamber 8 gradually increase. When the pressure inside the gas-liquid mixing chamber 8 is higher than the external pressure, the high-speed rotating micro-nano bubbles are ejected from the micro-nano bubble outlet 10 under the drive of the pressure difference.

[0068] Further, adjust the ejection speed V3 of the micro-nano bubbles by adjusting the power of the high-speed stirrer 9. When V3 = V / cosα, the micro-nano bubbles have a high enough speed to break through the turbulent boundary layer and enter the potential flow region outside the wake boundary layer. The micro-nano bubbles propagate downstream along the streamline 11 of the vehicle 1. The dissolution rate of the micro-nano bubbles in water can exceed 85%, and they remain in the water in the form of bubbles for a long time to form a micro-nano gas curtain 12. The micro-nano gas curtain 12 is annular and wraps around the propeller 2, which can reduce the far-field radiation noise of the propeller 2, avoid the detection and attack of underwater equipment such as sonar and torpedoes, and improve the stealth performance of large surface ships.

[0069] In one embodiment, the vehicle 1 is a large surface ship, and the gas inlet 6 is arranged above the waterline 14 of the large surface ship, and the air is the gas source.

[0070] Further, start the propeller 2 and the high-speed stirrer 9. The high-speed stirrer 9 forms a low-pressure area in the gas-liquid mixing chamber 8. The gas enters the gas-liquid mixing chamber 8 through the gas charging inlet 6, and the liquid enters the gas-liquid mixing chamber 8 through the water inlet 7. The gas and the liquid are fully mixed in the gas-liquid mixing chamber 8 to form a gas-liquid mixed fluid. The gas-liquid mixed fluid rotates at high speed under the action of pressure, and a negative pressure axis is formed in the middle of the gas-liquid mixing chamber 8. High-speed and strong shearing and high-frequency pressure pulsations are generated at the gas-liquid contact interface to form an artificial extreme condition. Under this condition, a large number of micron-sized and nano-sized bubbles are generated, collectively referred to as micro-nano bubbles.

[0071] Further, the gas and liquid in the gas-liquid mixing chamber 8 gradually increase. When the pressure inside the gas-liquid mixing chamber 8 is higher than the external pressure, the high-speed rotating micro-nano bubbles are ejected from the micro-nano bubble outlet 10 under the drive of the pressure difference.

[0072] Furthermore, by adjusting the power of the high-speed stirrer 9, the ejection speed V3 of the micro-nano bubbles is adjusted. When V3 = V / cosα, the micro-nano bubbles have a high enough speed to break through the turbulent boundary layer and enter the potential flow region outside the circumfluence boundary layer. The micro-nano bubbles propagate downstream along the streamline 11 of the vehicle 1. The dissolution rate of the micro-nano bubbles in water can exceed 85%, and they remain in the water in the form of bubbles for a long time, forming a micro-nano air curtain 12. The micro-nano air curtain 12 wraps around the propeller 2 and is fan-shaped, which can reduce the far-field radiation noise of the propeller 2, avoid the detection and attack of underwater equipment such as sonar and torpedoes, and improve the stealth performance of large surface ships.

[0073] Furthermore, by using the negative pressure axis generated by the high-speed stirrer 9, the gas and seawater are fully mixed, and under the artificially created extreme conditions, a large number of micron-sized and nano-sized bubbles are continuously generated. The dissolution rate of the micro-nano bubbles in water exceeds 85%, and they remain in the water in the form of bubbles for a long time, which is the key to the long-term and stable existence of the air curtain around the propeller 2.

[0074] Under the combined action of the adsorption of the negative pressure axis generated by the high-speed stirrer 9 on the gas and seawater and the one-way valves of the gas inlet 6 and the water inlet 7, the gas and seawater continuously enter the gas-liquid mixing chamber 8. When the pressure inside the gas-liquid mixing chamber 8 is higher than the external pressure, the gas-liquid mixed fluid is ejected from the micro-nano bubble outlet 10 under the drive of the pressure difference.

[0075] Due to the very high ejection speed of the gas-liquid mixed fluid, the gas-liquid mixed fluid carries the micro-nano bubbles out of the boundary layer and enters the potential flow region outside the circumfluence boundary layer. The micro-nano bubbles propagate downstream along the streamline 11 of the vehicle 1, and a relatively stable micro-nano air curtain 12 is formed. Among them, the ejection speed of the micro-nano bubbles is extremely crucial, and the inclined ejection speed will not affect the total resistance. The ejection speed should be high enough to break through the bondage of the circumfluence boundary layer. Otherwise, the micro-nano bubbles will not be able to enter the potential flow region, but will quickly dissipate under the action of turbulent dissipation and enter the propeller disk surface of the propeller 2, which may increase the number of gas nuclei and pose a risk of early onset of tip vortex cavitation.

[0076] Using multi-band and fixed-intensity sound waves, the sound insulation amount of the micro-nano air curtain 12 is calculated. Without considering the scattering and absorption effects of the micro-nano bubbles and only considering the noise transmission loss caused by the acoustic impedance of the micro-nano air curtain 12, a sound insulation amount of up to 30 dB can be achieved in the frequency band of 100 Hz to 10 kHz. It has the technical characteristics of simple structure, easy implementation, significant noise reduction effect, and no reduction in propulsion efficiency.

[0077] A method for reducing the noise of a propeller micro-nano air curtain driven by pressure difference includes the following steps:

[0078] Start the propeller 2, and the forward speed of the vehicle 1 is V;

[0079] Turn on the high-speed stirrer 9. The gas enters the gas-liquid mixing chamber 8 through the gas inlet 6, and the liquid enters the gas-liquid mixing chamber 8 through the water inlet 7 to form a gas-liquid mixed fluid. The gas-liquid mixed fluid rotates at a high speed under the action of pressure and forms a negative pressure axis in the middle of the gas-liquid mixing chamber 8, generating high-speed and strong shear and high-frequency pressure pulsations at the gas-liquid contact interface, creating an artificial extreme condition. Under this condition, a large number of micro-scale and nano-scale bubbles are generated, collectively referred to as micro-nano bubbles.

[0080] As the high-speed stirrer 9 rotates, the gas and liquid in the gas-liquid mixing chamber 8 gradually increase. When the pressure inside the gas-liquid mixing chamber 8 is higher than the external pressure, the high-speed rotating micro-nano bubbles are ejected from the micro-nano bubble outlet 10 under the drive of the pressure difference. The ejection speed of the micro-nano bubbles from the micro-nano bubble outlet 10 is V3.

[0081] Adjust the ejection speed V3 of the micro-nano bubbles by adjusting the power of the high-speed stirrer 9 so that V3 = V / cosα, enabling the micro-nano bubbles to have a high enough speed to break through the turbulent boundary layer and enter the potential flow region outside the circumfluence boundary layer.

[0082] The micro-nano bubbles propagate downstream along the streamline 11 of the vehicle 1. The dissolution rate of the micro-nano bubbles in water exceeds 85%, and they remain in the water in the form of bubbles for a long time, forming a micro-nano gas curtain 12 that wraps around the propeller 2.

[0083] The radiated noise of the propeller 2 passes through the micro-nano gas curtain 12, and the acoustic wave transmission loss caused by impedance can reduce the far-field radiated noise of the propeller 2 and improve the acoustic performance of the vehicle 1.

[0084] The above description is an explanation of the present invention, not a limitation of the invention. The scope defined by the present invention is referred to the claims. Any form of modification can be made within the protection scope of the present invention.

Claims

1. A differential pressure-driven propeller micro-nano air curtain noise reduction system, characterized in that Comprising: A gas-liquid mixing chamber (8), arranged in the internal space at the tail of the vehicle (1); A high-speed stirrer (9), arranged in the gas-liquid mixing chamber (8) for generating micro-nano bubbles; A gas inlet (6), arranged on the gas-liquid mixing chamber (8) and communicated with a gas source; A water inlet (7), arranged on the gas-liquid mixing chamber (8) with a diameter of D1; A micro-nano bubble outlet (10), arranged on the gas-liquid mixing chamber (8) for ejecting micro-nano bubbles, with a diameter of D2. The tangent of the profile line at the micro-nano bubble outlet (10) forms an angle α with the central axis (13) of the vehicle (1), and the angle between the micro-nano bubble outlet (10) and the central axis (13) of the vehicle (1) is -α; Wherein, a propeller (2) is arranged outside the tail of the vehicle (1); the center distance between the water inlet (7) and the micro-nano bubble outlet (10) is D3, and 6×D1 > D3 > 3×D2; When the ejection speed V3 of the micro-nano bubbles = V / cosα, the micro-nano bubbles enter the potential flow region, and the micro-nano bubbles propagate downstream along the streamline (11) of the vehicle (1) to form a micro-nano gas curtain (12) wrapping around the propeller (2).

2. The pressure-difference-driven propeller micro-nano air curtain noise reduction system according to claim 1, characterized in that: The micro-nano bubbles are micron-sized and nano-sized bubbles.

3. A differential-pressure-driven propeller micro-nano air curtain noise reduction system according to claim 1, characterized in that: The vehicle (1) is an underwater vehicle, and the gas source is a liquid nitrogen storage tank (3), and the liquid nitrogen storage tank (3) is communicated with the gas inlet (6).

4. The pressure-difference-driven propeller micro-nano air curtain noise reduction system according to claim 3, wherein: The liquid nitrogen storage tank (3) is arranged inside the underwater vehicle. An airtight piston (5) is arranged in the liquid nitrogen storage tank (3), and the airtight piston (5) is driven to move by a driving mechanism (4).

5. A differential pressure-driven propeller micro-nano air curtain noise reduction system according to claim 1, characterized in that: The vehicle (1) is a large surface ship, and the gas inlet (6) is arranged above the waterline (14) of the large surface ship, and air is the gas source.

6. The pressure-difference-driven propeller micro-nano air curtain noise reduction system according to claim 1, wherein: The angle α between the micro-nano bubble outlet (10) and the central axis (13) of the vehicle (1) ranges from 10° to 45°.

7. The pressure-difference-driven propeller micro-nano air curtain noise reduction system according to claim 3, characterized in that: The micro-nano gas curtain (12) is annular.

8. The pressure difference-driven propeller micro-nano air curtain noise reduction system according to claim 5, characterized in that: The micro-nano gas curtain (12) is fan-shaped.

9. The pressure-difference-driven propeller micro-nano air curtain noise reduction system according to claim 1, wherein: One-way valves capable of flowing into the gas-liquid mixing chamber (8) are arranged at both the gas inlet (6) and the water inlet (7), and a one-way valve capable of flowing out of the vehicle (1) is arranged at the micro-nano bubble outlet (10).

10. A pressure difference-driven propeller micro-nano air curtain noise reduction method, which uses a pressure difference-driven propeller micro-nano air curtain noise reduction system described in any one of claims 1-9, characterized in that, Including the following steps: Start the propeller (2), and the forward speed of the vehicle (1) is V; Start the high-speed stirrer (9). The gas enters the gas-liquid mixing chamber (8) through the gas inlet (6), and the liquid enters the gas-liquid mixing chamber (8) through the water inlet (7) to form a gas-liquid mixed fluid. The gas-liquid mixed fluid rotates at a high speed under the action of pressure, and a negative pressure axis is formed in the middle of the gas-liquid mixing chamber (8). High-speed and strong shear and high-frequency pressure pulsations are generated at the gas-liquid contact interface to form artificial extreme conditions. Under such conditions, a large number of micron-sized and nano-sized bubbles are generated, collectively referred to as micro-nano bubbles; As the high-speed stirrer (9) rotates, the gas and liquid in the gas-liquid mixing chamber (8) gradually increase. When the pressure inside the gas-liquid mixing chamber (8) is higher than the external pressure, the high-speed rotating micro-nano bubbles are ejected from the micro-nano bubble outlet (10) under the drive of the pressure difference, and the ejection speed of the micro-nano bubbles from the micro-nano bubble outlet (10) is V3; Adjust the ejection speed V3 of micro-nano bubbles by adjusting the power of the high-speed stirrer (9) so that V3 = V / cosα, enabling the micro-nano bubbles to have a high enough speed to break through the turbulent boundary layer and enter the potential flow region outside the circumfluence boundary layer; The micro-nano bubbles propagate downstream along the streamline (11) of the vehicle (1). The dissolution rate of the micro-nano bubbles in water exceeds 85%, and they remain in the water in the form of bubbles for a long time, forming a micro-nano air curtain (12) that wraps around the propeller (2); The radiation noise of the propeller (2) passes through the micro-nano air curtain (12), and the acoustic wave transmission loss caused by impedance can reduce the far-field radiation noise of the propeller (2) and improve the acoustic performance of the vehicle (1).

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