A rotary body aircraft air film layer drag reduction device, a preparation method and an application thereof

Abstract

This invention discloses a drag reduction device, its preparation method, and its application for the air film layer of a rotating vehicle, belonging to the field of drag reduction technology. The drag reduction device includes an eccentric ventilation ring, which is composed of a porous eccentric ring and a superhydrophobic surface. The preparation method of the drag reduction device comprises the following steps: based on a porous superhydrophobic horizontal plate ventilation experiment, obtaining a curve and formula showing the pressure difference between the two sides of the plate as a function of the plate thickness; calculating the radial thickness of the eccentric ventilation ring; calculating the inner ring radius of curvature of the eccentric ventilation ring; processing the porous eccentric ring based on the calculated design parameters; and subjecting the processed porous eccentric ring to superhydrophobic treatment to obtain the eccentric ventilation ring. This invention is applicable to drag reduction through ventilation on the surface of rotating bodies, providing long-lasting drag reduction and good drag reduction effect.

Description

Technical Field

[0001] This invention belongs to the field of drag reduction technology, specifically relating to a drag reduction device for the air film layer of a rotating vehicle, its preparation method, and its application. Background Technology

[0002] During navigation, underwater vehicles are subject to flow resistance, represented by frictional resistance and pressure difference resistance. Since underwater vehicles are usually rotating bodies with a large length-to-slenderness ratio, the frictional resistance generated by their surface in direct contact with the fluid accounts for more than 80% of the total resistance. Therefore, reducing surface frictional resistance is an important means for underwater vehicles to increase speed and range, as well as save energy and reduce emissions.

[0003] Superhydrophobic surface drag reduction technology utilizes unique micro / nano interface effects. Superhydrophobic surfaces can adsorb a gas film underwater, exhibiting multiphase flow, boundary slip, and reduced turbulent kinetic energy near the wall, thus decreasing wall friction. Maintaining the gas film morphology of the superhydrophobic surface is a prerequisite for effective drag reduction. However, the gas film on superhydrophobic surfaces can be disrupted under water pressure, pressure fluctuations, and fluid shearing, thereby losing its drag-reducing effect. Therefore, it is necessary to improve the stability of superhydrophobic surfaces.

[0004] Existing research has confirmed that using superhydrophobic surfaces in conjunction with artificial ventilation can effectively reduce the contact area between the surface of a vehicle and water, replacing non-slip walls with partially slippery walls, thereby producing a significant drag reduction effect. Most methods of artificial ventilation to superhydrophobic surfaces are micropore arrays or slit ventilation, but it is difficult to keep the micropore size consistent. In addition, under the influence of water pressure, the small ventilation volume makes it difficult for the gas to be uniformly ventilated across the entire plane.

[0005] Most drag reduction techniques using ventilation are designed for flat surfaces and ship models. While experimental studies on flat surfaces demonstrate significant drag reduction potential, they are less commonly applied to rotating bodies, which offer a more practical shape compared to flat surfaces and ship models. For rotating body surfaces, existing ventilation drag reduction technologies still have certain shortcomings. Their drag reduction characteristics are greatly influenced by the bubble flow morphology. At low flow velocities, bubbles easily float upwards and detach from the boundary layer due to buoyancy, thus failing to achieve drag reduction and making them unsuitable for underwater rotating vehicle surfaces. Therefore, it is necessary to design a drag reduction device for underwater ventilation air film layers of rotating vehicles using a porous superhydrophobic material with a permeability gradient, to achieve uniform ventilation through the porous material and maintain the stability of the air film layer on the rotating body surface. Summary of the Invention

[0006] The technical problem to be solved:

[0007] To overcome the shortcomings of existing technologies, this invention provides a drag reduction device for air film layer of rotating vehicles, its preparation method, and its application. The drag reduction device is an eccentric ring designed based on an empirical formula for the change of pressure difference between the two sides of a flat plate with thickness. After the eccentric ring is processed, the inner and outer sides of the eccentric ring are treated with superhydrophobicity using an electrochemical etching method. The resulting porous superhydrophobic ventilating ring is suitable for ventilating and reducing drag on the surface of rotating bodies, with a long drag reduction duration and good drag reduction effect.

[0008] The technical solution of the present invention is: a drag reduction device for air film layer of a rotating vehicle, comprising an eccentric ventilation ring, wherein the eccentric ventilation ring is composed of an eccentric ring of porous material and a superhydrophobic treated surface;

[0009] The radial design thickness of the ring is:

[0010]

[0011] Among them, P max R is the maximum hydrostatic pressure difference when the eccentric ring is placed in water, R is the outer diameter of the ring (the specific value depends on the shape of the rotating vehicle), ρ is the density of the fluid in which the vehicle is located, θ is the angle between the line connecting a point on the circumference of the ring to the center and the perpendicular line, and k is a coefficient in the formula.

[0012] A further technical solution of the present invention is that the superhydrophobic treatment adopts an electrochemical corrosion method.

[0013] A method for preparing a drag reduction device for the air film layer of a rotating vehicle, comprising the following specific steps:

[0014] Based on the ventilation experiment of the porous superhydrophobic horizontal plate, the curve of the pressure difference between the two sides of the plate and the plate thickness and the formula of the pressure difference with the plate thickness were obtained.

[0015] Calculate the radial thickness of the eccentric venting ring;

[0016] Calculate the inner ring radius of curvature of the eccentric venting ring;

[0017] Based on the design parameters of the eccentric venting ring obtained from the above calculations, the porous eccentric ring is processed.

[0018] The processed porous eccentric ring is subjected to superhydrophobic treatment to obtain an eccentric ventilated ring.

[0019] A further technical solution of the present invention is: the experimental device for the ventilation experiment of the porous superhydrophobic horizontal plate includes: a left ventilation module and a right ventilation module symmetrically arranged, a gas mass flow indicator, a differential pressure measuring instrument, and an air pump;

[0020] The left ventilation module is a hollow cuboid structure with one open end. Its closed end is connected to an air pump through a pneumatic connector and a pneumatic hose, and a gas mass flow meter is installed on the pneumatic hose. A differential pressure gauge is installed on its side wall to measure the air pressure in the inner cavity.

[0021] The right ventilation module is a hollow cuboid structure with one open end. The opening is provided with a groove structure for installing the porous superhydrophobic horizontal plate to be tested. A differential pressure gauge is installed on its side wall to measure the air pressure in the inner cavity.

[0022] The open ends of the left and right ventilation modules are placed opposite each other, and the porous superhydrophobic horizontal plate to be tested is placed into the groove and then clamped and sealed.

[0023] A further technical solution of the present invention is as follows: The specific steps of the ventilation experiment of the porous superhydrophobic horizontal plate are as follows:

[0024] Based on the experimental requirements, multiple porous superhydrophobic horizontal plates with the same porosity but different thicknesses were selected.

[0025] A porous superhydrophobic horizontal plate to be tested is clamped and sealed between the left ventilation module and the right ventilation module;

[0026] Select a gas mass flow indicator, differential pressure measuring instrument, air pump, and connect them to the left / right ventilation module within the range of measurement.

[0027] After powering on the experimental setup, control the gas flow rate, observe the reading of the differential pressure gauge, and record the data.

[0028] After the test is completed, turn off the air pump and power supply, replace with a porous superhydrophobic horizontal plate of the next thickness, and repeat the cycle until all selected thicknesses have been measured.

[0029] A further technical solution of the present invention is: the formula for calculating the pressure difference on both sides of the plate is as follows:

[0030] ΔP=kδ

[0031] Where ΔP represents the pressure difference across the plate, k is a coefficient in the formula, and δ is the thickness of the plate.

[0032] A further technical solution of the present invention is: the formula for calculating the radial design thickness of the eccentric venting ring is as follows:

[0033]

[0034] Among them, P max R is the maximum hydrostatic pressure difference when the eccentric ring is placed in water, R is the outer diameter of the ring (the specific value depends on the shape of the rotating vehicle), ρ is the density of the fluid in which the vehicle is located, θ is the angle between the line connecting a point on the circumference of the ring to the center and the perpendicular line, and k is a coefficient in the formula.

[0035] A further technical solution of the present invention is: the formula for calculating the inner ring curvature radius of the eccentric venting ring is as follows:

[0036] R i =R-δ-γ

[0037] Wherein, γ is the base thickness of the eccentric venting ring.

[0038] A further technical solution of the present invention is as follows: The specific steps of the superhydrophobic treatment are as follows:

[0039] Prepare a 0.1 mol / L NaCl electrolyte solution, use a graphite ring as the cathode and an eccentric ventilated ring as the anode, adjust the voltage of the DC regulated power supply to 15V, and perform electrochemical micro-etching on the eccentric ventilated ring for 15 min.

[0040] The electrolyte was prepared by 300 mL of ethylene glycol, 1.5 g of NH4F and 6 mL of deionized water. A graphite ring was used as the cathode and an eccentric venting ring was used as the anode. The voltage of the DC regulated power supply was adjusted to 60 V. The eccentric venting ring was anodized for 3 hours.

[0041] A rotating vehicle includes a head section, a film film drag reduction device, a mid-section of the vehicle, and a ventilation system installed inside the mid-section. The film film drag reduction device is nested and fixed between a nozzle mounting base and a head section.

[0042] The ventilation system includes a gas cylinder, a pressure gauge, and a flow controller. The gas cylinder is connected to a nozzle through a pneumatic hose to deliver gas to the eccentric ventilation ring of the air film layer drag reduction device, and then outputs the gas to the annular surface of the vehicle through tiny air holes in the eccentric ventilation ring.

[0043] The ventilation rate is adjusted according to the incoming flow velocity to maintain the stability of the air film layer on the surface of the eccentric ventilation ring and achieve uniform gas ventilation.

[0044] Beneficial effects

[0045] The beneficial effects of the present invention are as follows: Compared with existing devices and corresponding technologies, the present invention has the following characteristics:

[0046] 1. The present invention proposes an underwater air film layer drag reduction device for rotating vehicles based on the permeability gradient of porous superhydrophobic materials. It belongs to the field of drag reduction technology of annular adjustable injection device and control method suitable for underwater vehicles. The porous superhydrophobic air ring is suitable for air ventilation and drag reduction on the surface of rotating bodies, with long drag reduction duration and good drag reduction effect.

[0047] 2. When a porous superhydrophobic ventilated ring is placed in water, a thin gas film forms on its surface. After aeration, the gas is affected by buoyancy, resulting in uneven aeration. The designed eccentric ring achieves uniform aeration. Due to the porous nature of the material, the interconnected micropores provide ample ventilation points, reducing the effect of surface tension. Therefore, the influence of surface tension does not need to be considered when designing the eccentric ring.

[0048] 3. The control device for regulating the injection rate of the air film layer of the aircraft is located in the middle of the aircraft body and consists of a gas cylinder, a pressure gauge, a flow controller, and a pneumatic hose. It observes the morphology of the air film layer on the porous annular surface under different incoming flows, dynamically adjusts the gas cylinder ventilation rate, maintains the stability of the air film layer on the porous annular surface, and achieves uniform gas ventilation. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the design principle of the porous superhydrophobic ventilated ring provided by the present invention;

[0050] Figure 2 A diagram of the porous superhydrophobic horizontal plate ventilation experimental device provided by the present invention;

[0051] Figure (a) shows the overall view of the ventilation experimental device; Figure (b) shows a detailed view of the ventilation device.

[0052] Figure 3 The graph shows the variation of the pressure difference across the two sides of the porous superhydrophobic horizontal plate provided by the present invention with its thickness.

[0053] In the figure: the horizontal axis represents the thickness of the plate, and the vertical axis represents the pressure difference;

[0054] Figure 4 The design diagram (a) of the medium-sized eccentric ring and the design diagram (b) of the small-sized porous eccentric ring with a ventilation rate of 6 ml / s provided by the present invention;

[0055] Figure 5 This is a schematic diagram of an annular adjustable jet device suitable for a vehicle according to the present invention;

[0056] Figure 6 The drag reduction effect diagram of the small-particle-size porous superhydrophobic ventilated ring provided by the present invention;

[0057] Explanation of reference numerals in the attached drawings: 1. Air pump, 2. Gas mass flow indicator, 3. Clamping device, 4. DC voltmeter, 5. Differential pressure measuring instrument, 6. Gas cylinder, 7. Pressure gauge, 8. Flow controller, 9. Mid-section of the vehicle body, 10. Nozzle mounting base, 11. Vent hole, 12. Porous superhydrophobic venting ring, 13. Head connection section, 14. Head of the vehicle body. Detailed Implementation

[0058] The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the invention, and should not be construed as limiting the invention.

[0059] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0060] Existing airflow drag reduction technologies are highly susceptible to the influence of bubble flow morphology. At low flow velocities, bubbles easily float upwards and detach from the boundary layer due to buoyancy, thus failing to achieve drag reduction and rendering them unsuitable for underwater rotating vehicle surfaces. This invention provides an air film layer drag reduction device for rotating vehicles, comprising an eccentric airflow ring. The eccentric airflow ring is composed of a porous material and a superhydrophobic surface. The air film layer drag reduction device is designed based on an empirical formula for the pressure difference across a flat plate as a function of thickness. First, based on the curve and empirical formula obtained from the airflow experiment of a porous superhydrophobic horizontal plate, the formula for the circumferential curvature of the inner ring of the eccentric ring as a function of the central angle is derived. The outer ring of the eccentric ring is a circle with radius R, and the closed region between the inner and outer rings is the designed eccentric ring. After the eccentric ring is processed, the inner and outer sides of the eccentric ring are treated with superhydrophobicity using an electrochemical etching method to obtain a porous superhydrophobic eccentric ventilated ring.

[0061] The method for preparing the air film layer drag reduction device for the rotating vehicle is characterized by the following specific steps:

[0062] Based on the ventilation experiment of the porous superhydrophobic horizontal plate, the curve of the pressure difference between the two sides of the plate and the plate thickness and the formula of the pressure difference with the plate thickness were obtained.

[0063] Calculate the radial thickness of the eccentric venting ring;

[0064] Calculate the inner ring radius of curvature of the eccentric venting ring;

[0065] Based on the design parameters of the eccentric venting ring obtained from the above calculations, the porous eccentric ring is processed.

[0066] The processed porous eccentric ring is subjected to superhydrophobic treatment to obtain an eccentric ventilated ring.

[0067] Specifically, the experimental apparatus for the ventilation experiment of the porous superhydrophobic horizontal plate includes: a symmetrically arranged left ventilation module and a right ventilation module, a gas mass flow indicator, a differential pressure measuring instrument, and an air pump; the left ventilation module is a hollow cuboid structure with one open end, and its closed end is connected to the air pump through a pneumatic connector and a pneumatic hose, and a gas mass flow indicator is installed on the pneumatic hose; a differential pressure measuring instrument is installed on its side wall to measure the air pressure in the inner cavity; the right ventilation module is a hollow cuboid structure with one open end, and a groove structure for installing the porous superhydrophobic horizontal plate to be tested is provided at its opening; a differential pressure measuring instrument is installed on its side wall to measure the air pressure in the inner cavity; the open ends of the left and right ventilation modules are placed opposite each other, and the porous superhydrophobic horizontal plate to be tested is placed into the groove and clamped and sealed.

[0068] Specifically, the specific steps of the ventilation experiment of the porous superhydrophobic horizontal plate are as follows:

[0069] Based on the experimental requirements, multiple porous superhydrophobic horizontal plates with the same porosity but different thicknesses were selected.

[0070] A porous superhydrophobic horizontal plate to be tested is clamped and sealed between the left ventilation module and the right ventilation module;

[0071] Select a gas mass flow indicator, differential pressure measuring instrument, air pump, and connect them to the left / right ventilation module within the range of measurement.

[0072] After powering on the experimental setup, control the gas flow rate, observe the reading of the differential pressure gauge, and record the data.

[0073] After the test is completed, turn off the air pump and power supply, replace with a porous superhydrophobic horizontal plate of the next thickness, and repeat the cycle until all selected thicknesses have been measured.

[0074] Specifically, the parameter calculation steps for the eccentric venting ring are as follows:

[0075] Step 1: After the measurement is completed, the experimental data of different thicknesses at the same rate are organized, a linear curve is fitted, and the formula for the change of pressure difference with the thickness of the plate is obtained as follows:

[0076] ΔP=kδ

[0077] Where ΔP represents the pressure difference across the plate, k is a formula coefficient, and δ is the plate thickness;

[0078] Step 2: The relationship between pressure difference and plate thickness was obtained through plate aeration experiments. Based on this, an eccentric ring was designed to counteract the hydrostatic pressure difference, achieving uniform aeration underwater. maxThe maximum hydrostatic pressure difference when the porous ring is placed in water is generally the difference in hydrostatic pressure between the upper and lower ends of the ring. ΔP' is the pressure difference at any point on the circumference of the porous ring. This pressure difference needs to be compensated by increasing the thickness. By making ΔP and ΔP' equal, we obtain the formula for the thickness of the porous ring as a function of the center angle. R is the outer diameter of the ring, the specific value of which depends on the shape of the rotating vehicle. ρ is the density of the fluid in which the vehicle is located. θ is the angle between the line connecting a point on the circumference of the ring to the center and the perpendicular line. δ' is the designed thickness of the ring.

[0079] ΔP'=P max -ρg(R+R·cosθ)

[0080] ΔP=ΔP'

[0081]

[0082] Step 3: Inner ring curvature radius R i Subtract the design thickness δ' and the base thickness γ from the outer ring radius R. The outer ring is a circle with radius R. The final design formula for the inner ring curvature radius of the eccentric ring is as follows:

[0083] R i =R-δ-γ

[0084] Specifically, the superhydrophobic treatment method is as follows:

[0085] Step 1: Prepare a 0.1 mol / L NaCl electrolyte solution, use a graphite ring as the cathode and an eccentric ventilated ring as the anode, adjust the voltage of the DC regulated power supply to 15V, and perform electrochemical micro-etching on the eccentric ventilated ring for 15 minutes.

[0086] Step 2: The electrolyte is prepared by 300 mL of ethylene glycol, 1.5 g of NH4F and 6 mL of deionized water. A graphite ring is used as the cathode and an eccentric venting ring is used as the anode. The voltage of the DC regulated power supply is adjusted to 60 V. The eccentric venting ring is anodized for 3 hours.

[0087] In application, the assembled control device is placed inside the middle section of the vehicle. Then, the head of the vehicle, the porous superhydrophobic eccentric ventilation ring, and the middle section of the vehicle are assembled in sequence. The model is placed in a water tunnel and an incoming flow velocity is set. The ventilation rate is adjusted according to the incoming flow velocity to maintain the stability of the gas film layer on the surface of the eccentric ventilation ring, thereby achieving uniform gas ventilation.

[0088] The above technical solution will be further explained below with reference to the accompanying drawings:

[0089] This embodiment describes a control device based on jet rate that can achieve uniform circumferential airflow in a porous superhydrophobic ventilated annulus. The description is based on its drag reduction device and control method.

[0090] For air film layer drag reduction devices, see reference. Figure 1 Based on a uniform concentric ring, an eccentric ring is designed. The porous ring placed in water has the maximum hydrostatic pressure difference P. max =P2-P1, where R is the radius of the porous ring, P1 is the pressure at the bottom of the porous ring, and P2 is the pressure on the upper surface of the porous ring. Based on the aircraft model, the outer diameter of the porous ring is determined to be 60mm, and the pressure at the top of the ring needs to be compensated for by its thickness, resulting in 600pa.

[0091] P max =P2-P1=2R·ρg=2*0.03*1000*10=600pa

[0092] Based on the aeration experimental data of the porous superhydrophobic horizontal plate, an empirical formula for the pressure difference across the two sides of the plate as a function of the plate thickness was obtained: ΔP = kδ. The hydrostatic pressure difference at any point on the ring from the top is ΔP' = P. max -ρg(R+R·cosθ), the pressure difference value that needs to be compensated for by thickness is equal to the pressure difference value obtained by the formula of pressure difference changing with plate thickness, that is, ΔP=ΔP'.

[0093] The formula for thickness δ as a function of angle θ is derived. The inner ring radius of curvature is the outer ring radius minus the base thickness and design thickness. The base thickness of the ring is 3mm, so the formula for the inner ring radius of curvature is R=0.03-0.003-δ.

[0094] For the ventilation test of the porous superhydrophobic horizontal plate, please refer to the diagram of the test setup. Figure 2 The porous superhydrophobic horizontal plate ventilation experimental device mainly consists of an air pump (1), a gas mass flow controller (2), a clamping device (3), a DC voltmeter (4), and a differential pressure measuring instrument (5). The air pump is connected to the gas flow mass indicator via a pneumatic hose. The porous superhydrophobic horizontal plate is embedded in the ventilation device, which requires custom-made groove shapes to accommodate different thicknesses of the plate. The differential pressure measuring instrument is connected to the left inlet and right outlet of the clamping device. The gas flow mass indicator is adjusted to control the gas flow rate at the inlet. To test and verify the assembled ventilation device, the air pump and DC power are turned on, the flow controller is set, and the reading of the differential pressure measuring instrument is observed and recorded. After testing the same thickness, the air pump and DC power are turned off, the porous superhydrophobic horizontal plate is removed from the clamping device, and the same operation is repeated for a different thickness.

[0095] Reference Figure 3Taking an airflow rate of 6 ml / s as an example, experimental data on the pressure difference across a porous superhydrophobic horizontal plate of the same particle size but different thicknesses were plotted as a scatter plot and fitted. The porous superhydrophobic horizontal plate has dimensions of 25 mm x 25 mm. The two particle sizes are medium and small, and five thicknesses were set for each particle size: 3 mm, 6 mm, 9 mm, 12 mm, and 15 mm. Comparison of the fitting results showed that linearity best matched the experimental pattern. Note that the linear curve needs to be forced to pass through the origin; otherwise, it does not satisfy the condition that the pressure is zero when the wall thickness is zero, which is inconsistent with the actual situation.

[0096] Based on the fitting results, a formula for the pressure difference across the porous superhydrophobic horizontal plate as a function of the plate thickness is obtained, where ΔP represents the pressure difference across the plate, k is a coefficient in the formula, and δ is the thickness of the annulus:

[0097] ΔP=kδ

[0098] The linear formula for fitting medium-sized particles is ΔP = 27547δ, with coefficient k equal to 27547. The linear formula for fitting small-sized particles is ΔP = 109927δ, with coefficient k equal to 109927.

[0099] refer to Figure 4 The formula for the variation of the thickness of medium-sized grains with the center angle is:

[0100] δ1=-0.01089cosθ+0.011

[0101] The formula for the variation of small particle thickness with the center angle is:

[0102] δ² = -0.0027cosθ + 0.0273

[0103] Inner ring radius of curvature R i Subtract the design thickness δ and the foundation thickness γ from the outer ring radius R. The foundation thickness is 0.003m. The final design formula for the inner ring curvature radius is as follows:

[0104] R i =R-δ-γ

[0105] The formula for the inner ring curvature radius of medium-sized particles is:

[0106] R1=R-δ1-0.003=0.057-δ1=0.01089cosθ+0.01611

[0107] The formula for the inner ring curvature radius of small particle size is:

[0108] R2=R-δ2-0.003=0.057-δ2=0.0027cosθ+0.0243

[0109] The inner ring curve is drawn by the formula, and the outer ring curve is a circle with a radius of 30mm. The specific shape of the eccentric ring is the closed area surrounded by the inner and outer rings.

[0110] Reference Figure 5 As shown, for the water tunnel experiment of the vehicle model, the structure from right to left is as follows: mid-section 9, nozzle mounting base 10, vent 11, porous superhydrophobic venting ring 12, head connecting section 13, and head 14. The nozzle mounting base 10 is threadedly connected to the mid-section 9. The porous superhydrophobic venting ring 12 has a 2mm step on its outer side and is nested between the nozzle mounting base 10 and the head connecting section 13. A rubber gasket is placed on the contact surface to ensure airtightness. Gas is delivered to the vent 11 through a pneumatic hose and enters the flow field through the tiny pores of the porous superhydrophobic venting ring 12. The nut is screwed in to its tightest position, at which point it fits snugly against the head connecting section. The head 14 is threadedly connected to the head connecting section 13.

[0111] The gas source for regulating the gas injection rate includes a gas cylinder 6, a pressure gauge 7, and a gas mass flow controller 8. The gas cylinder outputs gas to the vent 11 through a pneumatic hose, and the pressure gauge 7 and the gas mass flow controller 8 are installed on the connecting pipeline to measure the ventilation pressure and control the gas flow rate, respectively. Based on the gas film state on the annular wall, the morphology of the gas film is regulated by adjusting the ventilation rate of the gas cylinder to avoid insufficient or excessive ventilation that could cause the gas film to detach, thus maintaining the stability of the gas film and enabling it to perform its drag-reducing function.

[0112] To investigate the effect of porous superhydrophobic venting annexes on drag reduction of aeroplane surfaces, drag reduction was tested at different ventilation rates for four flow velocities. (Reference) Figure 6 The graphs show the drag reduction ratio of the superhydrophobic surface as a function of the airflow rate Q at flow velocities u of 2 m / s, 3 m / s, 5 m / s, and 7 m / s. It can be observed that as the airflow rate increases, the drag reduction ratio of the vehicle surface at different flow velocities first increases and then decreases.

[0113] The drag reduction rate varies with ventilation rate under different flow rates, exhibiting two different patterns. At low flow rates (0–50 ml / s), the drag reduction effect at u = 3 m / s is better than that at the other three flow rates, achieving the optimal drag reduction effect with a drag reduction rate of up to 27%.

[0114] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A method for preparing a drag reduction device for a rotating vehicle's film layer, characterized in that: The drag reduction device includes an eccentric venting ring, which is composed of an eccentric ring made of porous material and a superhydrophobic treated surface. The specific steps of the preparation method are as follows: Based on the ventilation experiment of the porous superhydrophobic horizontal plate, the curve of the pressure difference across the plate as a function of the plate thickness and the formula for the pressure difference as a function of the plate thickness were obtained; the formula for calculating the pressure difference across the plate is as follows: wherein, represents the difference in pressure between the two sides of the plate, k is a formula coefficient, is the thickness of the plate; Calculate the radial thickness of the eccentric venting ring; the hydrostatic pressure difference between any point on the ring and the top is [value missing]. The differential pressure value that needs to be compensated for by thickness is equal to the differential pressure value obtained from the formula for differential pressure varying with plate thickness, i.e. The radial design thickness of the ring is: in, R represents the maximum hydrostatic pressure difference when the eccentric ring is placed in water, and R is the outer diameter of the ring, the specific value of which depends on the shape of the rotating vehicle. The density of the fluid in which the vehicle is located. Let be the angle between the line connecting a point on the circumference of the annulus to the center and the perpendicular line, and k be the coefficient of the formula; Calculate the inner ring radius of curvature of the eccentric venting ring; the formula for calculating the inner ring radius of curvature of the eccentric venting ring is as follows: wherein, is the base thickness of the eccentric venting toroid; Based on the design parameters of the eccentric venting ring obtained from the above calculations, the porous eccentric ring is processed. The processed porous eccentric ring is subjected to superhydrophobic treatment to obtain an eccentric ventilated ring.

2. The method of claim 1, wherein the method further comprises: The superhydrophobic treatment employs an electrochemical corrosion method.

3. The method of claim 1, wherein the method further comprises: The experimental setup for the ventilation experiment of the porous superhydrophobic horizontal plate includes: a left ventilation module and a right ventilation module arranged symmetrically, a gas mass flow indicator, a differential pressure measuring instrument, and an air pump; The left ventilation module is a hollow cuboid structure with one open end. Its closed end is connected to an air pump through a pneumatic connector and a pneumatic hose, and a gas mass flow meter is installed on the pneumatic hose. A differential pressure gauge is installed on its side wall to measure the air pressure in the inner cavity. The right ventilation module is a hollow cuboid structure with one open end. The opening is provided with a groove structure for installing the porous superhydrophobic horizontal plate to be tested. A differential pressure gauge is installed on its side wall to measure the air pressure in the inner cavity. The open ends of the left and right ventilation modules are placed opposite each other, and the porous superhydrophobic horizontal plate to be tested is placed into the groove and then clamped and sealed.

4. The method of claim 3, wherein the method further comprises: The specific steps of the porous superhydrophobic horizontal plate ventilation experiment are as follows: Based on the experimental requirements, multiple porous superhydrophobic horizontal plates with the same porosity but different thicknesses were selected. A porous superhydrophobic horizontal plate to be tested is clamped and sealed between the left ventilation module and the right ventilation module; Select a gas mass flow indicator, differential pressure measuring instrument, air pump, and connect them to the left / right ventilation module within the range of measurement. After powering on the experimental setup, control the gas flow rate, observe the reading of the differential pressure gauge, and record the data. After the test is completed, turn off the air pump and power supply, replace with a porous superhydrophobic horizontal plate of the next thickness, and repeat the cycle until all selected thicknesses have been measured.

5. The method of claim 1, wherein the method further comprises: The specific steps of the superhydrophobic treatment are as follows: Prepare a 0.1 mol / L NaCl electrolyte solution, use a graphite ring as the cathode and an eccentric ventilated ring as the anode, adjust the voltage of the DC regulated power supply to 15V, and perform electrochemical micro-etching on the eccentric ventilated ring for 15 min. The electrolyte was prepared by 300 mL of ethylene glycol, 1.5 g of NH4F and 6 mL of deionized water. A graphite ring was used as the cathode and an eccentric venting ring was used as the anode. The voltage of the DC regulated power supply was adjusted to 60 V. The eccentric venting ring was anodized for 3 hours.

6. A gyrating body vehicle, characterized by: The system includes a head section of the aircraft, a film layer drag reduction device prepared by the preparation method according to any one of claims 1-5, a mid-section of the aircraft, and a ventilation system installed inside the mid-section, wherein the film layer drag reduction device is nested and fixed between the nozzle mounting base and the head section. The ventilation system includes a gas cylinder, a pressure gauge, and a flow controller. The gas cylinder is connected to a nozzle through a pneumatic hose to deliver gas to the eccentric ventilation ring of the air film layer drag reduction device, and then outputs the gas to the annular surface of the vehicle through tiny air holes in the eccentric ventilation ring. The ventilation rate is adjusted according to the incoming flow velocity to maintain the stability of the air film layer on the surface of the eccentric ventilation ring and achieve uniform gas ventilation.

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