Stable thick air film underwater drag reduction structure based on bubble spontaneous rapid transportation and forming method

Abstract

The invention discloses a stable thick air film underwater resistance reduction structure based on bubble spontaneous rapid transportation and a forming method. The stable thick air film underwater resistance reduction structure comprises super-hydrophobic track structures which are arranged on a substrate side by side at equal intervals and used for forming an underwater resistance reduction air film. The super-hydrophobic track structure comprises a first track section and a second track section; bubbles are captured underwater through the first track section; the second track section comprises conical column array track sections which are arranged in series, have cycloid contour structures at the edges and are used for bubble transmission; transition arc contraction sections used for driving bubbles to flow between the first track section and the second track section or between the adjacent conical column array track sections are arranged at the connecting end of the first track section and the second track section and between the conical column array track sections. And a conical column array arranged on the upper surface of the conical column array track section is used for enabling flowing bubbles to form an air film. The problems that an existing ship underwater drag reduction structure is thin in formed air film, poor in air film stability and the like are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of surface drag reduction for underwater vehicles, and particularly to a stable thick gas film underwater drag reduction structure based on spontaneous rapid bubble transportation and a forming method thereof. Background Art

[0002] Underwater drag reduction of ships can significantly reduce energy consumption and greenhouse gas emissions during navigation, which is crucial for energy conservation, emission reduction, and sustainable development of humanity. In recent years, nature's organisms have given humans a lot of inspiration to try to solve this problem. Although artificial surfaces inspired by sharks and butterflies have a certain drag reduction ability, their drag reduction rates are not high enough, and the application of macroscopic array structures makes these surfaces vulnerable to adhesion by marine organisms, resulting in drag reduction loss or even increased drag. Compared with natural surfaces, bubble drag reduction relying on gas lubrication has a higher drag reduction rate because the shear friction at the solid-liquid boundary is reduced. However, the large escape of injected bubbles reduces the gas coverage area, leading to instability of the gas-liquid slip boundary and insufficient drag reduction efficiency, which affects its large-scale application in the marine industry.

[0003] Researchers have developed a tandem wedge-shaped wettability-patterned surface composed of an internal superhydrophobic region and an external superhydrophilic region to enhance the bubble capture ability and achieve spontaneous bubble transportation along the patterned surface (J. Mater. Chem. A, 2019, 7, 13567 - 13576); the existing paper (J. Mater. Chem. A, 2024, 12, 19268 - 19276) optimized the above tandem wedge pattern into a tandem cycloid structure based on the brachistochrone curve, with its interior still being superhydrophobic and its exterior still being superhydrophilic, to further improve the bubble capture efficiency and transportation speed. However, since constructing superhydrophilicity requires prior construction of microstructures, the introduction of superhydrophilic microstructures will increase the resistance of the superhydrophilic region; the existing paper (Nanoscale, 2025, 17, 10892–10900) only processed a tandem wedge-shaped wettability-patterned surface formed by a superhydrophobic pattern with a brachistochrone curve tandem cycloid to enhance the bubble capture ability and achieve spontaneous bubble transportation along the patterned surface (J. Mater. Chem. A, 2019, 7, 13567 - 13576), while the exterior is an untreated ordinary hydrophilic surface, improving the drag reduction effect. However, only micron-scale structures exist within the superhydrophobic pattern with a brachistochrone curve tandem cycloid, resulting in a relatively low gas film thickness maintaining the superhydrophobic state and poor gas film stability. To further improve the drag reduction ability, it is necessary to increase the gas film thickness.

[0004] In summary, the existing underwater drag reduction structures for ships have problems such as thin gas films formed, poor gas film stability, and thus poor underwater drag reduction effects. Summary of the Invention

[0005] The present invention provides a stable thick gas film underwater drag reduction structure based on spontaneous rapid transportation of bubbles and a forming method thereof to overcome the above technical problems.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] A stable thick gas film underwater drag reduction structure based on spontaneous rapid transportation of bubbles, including a superhydrophobic track structure that is arranged in parallel at equal intervals on a substrate and is used to form an underwater drag reduction gas film;

[0008] The superhydrophobic track structure includes a first track section and a second track section;

[0009] And the outer contour of the first track section is an arc-symmetric structure that shrinks from one end to the other end, and a cone column array is provided on the upper surface of the first track section for retaining bubbles underwater;

[0010] One end of the second track section is connected to one end of the first track section, and the second track section includes a plurality of cone column array track sections that are connected in series and have a cycloid profile structure at the edge for bubble transmission;

[0011] And a transition arc contraction section for driving the flow of bubbles between the first track section and the second track section or between adjacent cone column array track sections is provided between the connection end of the first track section and the second track section and between each cone column array track section;

[0012] The cone column array provided on the upper surface of the cone column array track section is used to capture flowing bubbles and spread them to form a gas film on the entire track.

[0013] Further, the transition arc radius of the transition arc contraction section is 1 mm;

[0014] And one end of the transition arc contraction section is connected to one end of the second track section, the other end of the transition arc contraction section is connected to one end of the first track section, or both ends of the transition arc contraction section are respectively connected to one end of adjacent cone column array track sections.

[0015] Further, the bottom radii of the cone columns in the cone column arrays provided on the cone column array track section and the first track section are both 100 - 300 μm;

[0016] The height of the cone columns is 350 - 450 μm;

[0017] The center distance between each cone column is 400 - 600 μm;

[0018] The bottom surface of the cone column array is 400 - 500 μm away from the upper surface of the substrate.

[0019] Further, the width ratio of both ends of the cycloid profile structure is equal to 0.8;

[0020] The length of the cycloid is 21 - 23 mm.

[0021] Furthermore, the spacing of the superhydrophobic track structure on the substrate is 4 - 4.5 mm.

[0022] A forming method for a stable thick gas film underwater drag reduction structure based on spontaneous and rapid bubble transportation specifically includes the following steps:

[0023] S1: Cover a layer of black polyethylene film on the substrate to obtain a combined substrate;

[0024] S2: Based on laser processing technology, according to the edge contour shape of the superhydrophobic track structure, perform a primary scanning process on the combined substrate to obtain a primary processed substrate;

[0025] And remove the black polyethylene film surrounded by the edge contour shape on the primary processed substrate;

[0026] S3: Once again, adopt laser processing technology to perform a scanning process on the substrate obtained in S2 for the cone - column array structure to obtain a secondary processed substrate;

[0027] And the laser parameters of the secondary processed substrate are the same as those of the primary scanning process;

[0028] S4: Immerse the secondary processed substrate in a fluorosilane solution for soaking, put the soaked secondary processed substrate into an oven for drying, and finally remove the remaining black polyethylene film to obtain the superhydrophobic track structure for forming the underwater drag reduction gas film.

[0029] Beneficial effects: The present invention provides a stable thick gas film underwater drag reduction structure and a forming method based on spontaneous and rapid bubble transportation. Bubbles are supplied through the first track section of the superhydrophobic track structure in water, and through the upper surface of the series - connected cone - column array track section, bubbles can be easily captured and spread to form a gas film. At the same time, through the cone - column array, free bubbles can be more easily captured to form large bubbles on the track to increase the thickness of the formed gas film. The gas film is extruded by the transition arc contraction section and transmitted to the next adjacent cone - column array track section, enabling the gas film to be rapidly transported on the second track section. At the same time, the high - speed transported large bubbles can continue to capture free bubbles in the advancing direction to further improve the underwater drag reduction effect through the gas film formed on the second track section. Description of the Drawings

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without any creative effort.

[0031] Figure 1 Schematic diagram of the stable thick gas film underwater drag reduction structure based on the spontaneous and rapid transportation of bubbles in the present invention;

[0032] Figure 2 Schematic diagram of the structure of the conical column array track section in this embodiment;

[0033] Figure 3 Schematic diagram of the transition arc contraction section in this embodiment;

[0034] Figure 4 Schematic diagram of the gas film formed by the underwater drag reduction structure in this embodiment;

[0035] Figure 5 Schematic diagram of the gas film formed by the comparative example in this embodiment;

[0036] Figure 6 Schematic diagram of the starting rotation angle and the ending rotation angle in this embodiment;

[0037] Figure 7 Schematic diagram of the contact angle / rolling angle between the superhydrophobic surface and the water droplet in this embodiment;

[0038] Figure 8 Schematic diagram of the contact angle between the ordinary aluminum surface and the gas film in water / water droplet in air in this embodiment;

[0039] Figure 9 Flowchart of the forming method of the stable thick gas film underwater drag reduction structure based on the spontaneous and rapid transportation of bubbles in the present invention.

[0040] In the figure: 1. Substrate; 2. Superhydrophobic track structure; 21. First track section; 22. Second track section; 221. Transition arc contraction section; 222. Cycloid profile structure; 3. Conical column array track section; 4. Conical column array. Detailed implementation manners

[0041] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some but not all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0042] This embodiment provides a stable thick gas film underwater drag reduction structure based on the spontaneous and rapid transportation of bubbles, as Figure 1As shown in the figure, it includes a superhydrophobic track structure 2 that is arranged side by side at equal intervals on the substrate 1 and is used to form an underwater drag-reducing air film. The structure between each superhydrophobic track structure 2 is a superhydrophilic track. Only by arranging the superhydrophobic track structure and the superhydrophilic track alternately can it be ensured that the air film covers the superhydrophobic track, rather than the entire aluminum sheet substrate;

[0043] Preferably, the spacing of the superhydrophobic track structure 2 on the substrate 1 is 4 - 4.5 mm;

[0044] The superhydrophobic track structure 2 includes a first track segment 21 and a second track segment 22;

[0045] Moreover, the outer contour of the first track segment 21 is an arc-symmetric structure that shrinks from one end to the other end, and a cone column array 4 is provided on the upper surface of the first track segment 21 for capturing air bubbles underwater (in addition, the air bubbles can be generated by an air pump provided outside the front of the tip of the first track segment 21); As Figure 7 shown in the figure, in this embodiment, the angle Q between the straight line corresponding to the chord of one side of the arc-symmetric structure and the preset perpendicular line is defined as the starting rotation angle: the value range is 159 - 161°, and the angle R between the straight line corresponding to the chord of the other side of the arc-symmetric structure and the preset perpendicular line is defined as the ending rotation angle: the value range is 179 - 181°;

[0046] One end of the second track segment 22 is connected to one end of the first track segment 21. As Figure 2 shown in the figure, the second track segment 22 includes a cone column array track segment 3 with a cycloid contour structure 222 at the edge arranged in series for air bubble transmission; Preferably, the bottom radii of the cone columns in the cone column array track segment 3 and the cone column array 4 provided on the first track segment 21 are both 100 - 300 μm;

[0047] The height of the cone columns is 350 - 450 μm;

[0048] The center distance between each cone column is 400 - 600 μm;

[0049] The bottom surface of the cone column array 4 is 400 - 500 μm away from the upper surface of the substrate 1;

[0050] In a specific embodiment, the method for obtaining the cycloid contour structure 222 of the cone column array track segment 3 is as follows: Based on a given center point A and a given radius, a characteristic circle is obtained. Randomly select any point on the characteristic circle as the cycloid contour feature point; Obtain the trajectory curve segment of the cycloid contour feature point moving in a given direction during the rolling process of the characteristic circle on the horizontal plane, that is, the brachistochrone curve of the cycloid contour feature point;

[0051] Taking the two end points of the trajectory curve segment as the starting points, intercepting curve segments with different distances in the opposite directions to obtain the intercepted characteristic outer contour line, and based on the characteristic outer contour line, symmetrically obtaining the symmetric contour feature according to the given center line, and defining the symmetric contour feature as the cycloid contour structure 222; preferably, the width ratio of both ends of the cycloid contour structure 222 is equal to 0.8; the cycloid length is 21-23 mm;

[0052] In this embodiment, the captured bubbles can be spread on the surface of the cone-column array track segment 3 through the cycloid contour structure 222 to form an air film. The interior of the track of the cone-column array track segment 3 also includes superhydrophobicity obtained through a low surface energy modification technique, so that the contact angle of water droplets in the air in the track and the contact angle of air bubbles in the water in the track are both greater than 150°; the outside of the track of the cone-column array track segment 3 is protected by a mask technique, so that the contact angle of water droplets in the air outside the track is 70°, and the contact angle of air bubbles in the water outside the track is 100°, and an air film can be formed through the superhydrophobic track structure 2 between the superhydrophilic tracks; in this embodiment, a superhydrophobic surface can be obtained through a low surface energy modification technique, and the contact angle and the rolling angle are only one data requirement for proving that this surface is a superhydrophobic surface; a polyethylene protective film is formed outside the track of the cone-column array track segment 3 through a mask technique, and the contact angle of the water droplets with the outside of the track is also to prove that the outside track does not have superhydrophobic characteristics, so as to prove that the polyethylene protective film protects the non-track part well during the processing steps. Among them, the processing methods of the low surface energy modification technique and the mask technique for the track surface of the cone-column array track segment 3 in this embodiment are all well-known technical means in the art and will not be elaborated here;

[0053] Moreover, a transition arc contraction section 221 for driving the flow of air bubbles between the first track segment 21 and the second track segment 22 or between adjacent cone-column array track segments 3 is provided at the connection end of the first track segment 21 and the second track segment 22 and between each cone-column array track segment 3;

[0054] In a specific embodiment, as Figure 3 shown, the transition arc radius of the transition arc contraction section 221 is 1 mm; one end of the transition arc contraction section 221 is connected to one end of the second track segment 22, and the other end of the transition arc contraction section 221 is connected to one end of the first track segment 21, or both ends of the transition arc contraction section 221 are respectively connected to one end of adjacent cone-column array track segments 3. Specifically, the transition arc contraction section 221 includes a first arc section 2210 and a second arc section 2211, and the first arc section 2210 and the second arc section 2211 are connected to form an S-shaped integral structure, and through this integral structure, the air film can be extruded to achieve spontaneous and rapid transmission on the upper surface of adjacent cone-column array track segments 3;

[0055] The cone-column array 4 provided on the upper surface of the cone-column array track section 3 is used to capture flowing bubbles and spread them to form an air film;

[0056] In the structure described in this embodiment, bubbles are supplied through the first track section of the superhydrophobic track structure in water, and through the upper surface of the series-connected cone-column array track section 3, bubbles can be easily captured and spread to form an air film. At the same time, through the cone-column array, free bubbles can be more easily captured to form large bubbles on the track to increase the thickness of the formed air film. The air film is squeezed by the transition arc contraction section and transmitted to the next adjacent cone-column array track section 3, enabling the air film to be quickly transported on the second track section. At the same time, the high-speed transported large bubbles can continue to capture free bubbles in the advancing direction to pass through the air film formed on the second track section. Therefore, the structure described in this embodiment has the characteristics of high bubble capture rate and stable air film, making it have excellent drag reduction effect.

[0057] A forming method of a stable thick air film underwater drag reduction structure based on spontaneous rapid transportation of bubbles, as Figure 9 shown, specifically includes the following steps:

[0058] S1: Cover a layer of black polyethylene film on the substrate 1 to obtain a combined substrate 1;

[0059] The substrate 1 is specifically an aluminum plate, and the size of the aluminum plate is 120*40*1 mm;

[0060] S2: Based on laser processing technology, according to the edge contour shape of the superhydrophobic track structure 2, the combined substrate 1 is scanned and processed once to obtain a once-processed substrate 1;

[0061] And the laser parameters for the once-scanning processing include:

[0062] Laser repetition frequency 20 GHz; scanning speed 600 mm / s; power 24 W;

[0063] And the black polyethylene film surrounded by the edge contour shape on the once-processed substrate 1 is removed;

[0064] S3: Again, adopt laser processing technology to perform scanning processing on the substrate obtained in S2 for the cone-column array 4 structure to obtain a twice-processed substrate 1;

[0065] And the laser parameters of the twice-processed substrate 1 are the same as those of the once-scanning processing;

[0066] S4: After immersing the twice-processed substrate 1 in a 1 wt% fluorosilane solution for one hour, it is placed in an oven and dried for 20 min, and finally the remaining black polyethylene film is removed, thereby obtaining the superhydrophobic track structure 2 for forming an underwater drag reduction air film.

[0067] Application Example 1: A stable thick gas film underwater drag reduction structure based on spontaneous and rapid bubble transportation, as Figure 1 shown. The superhydrophobic track structure 2 has a cycloid profile structure 222 with a series connection at the edge. The cycloid length required to obtain the cycloid profile structure is 22 mm. The aspect ratio between the narrow and wide ends of the connection between adjacent conical column array track segments 3 is 0.8. The arc radii of the first arc segment 2210 and the second arc segment 2211 are 1 mm. The bottom surface of the conical column array 4 is 400 μm deep from the upper surface of the substrate 1, that is, the depth of the second track segment 2. The track has a conical column array structure inside. The array structure is processed by laser etching. The height of the conical columns is 350 μm, the diameter is 200 μm, and the center distance between each conical column is 490 μm. The inside of the track of the conical column array track segment 3 also obtains superhydrophobicity through low surface energy modification technology, as Figure 6 shown, so that the contact angle of water droplets in the air in the track and the contact angle of air bubbles in the water in the track are both greater than 150°. The outside of the track of the conical column array track segment 3 is protected by a masking technology, so that the contact angle of water droplets in the air outside the track is 70°, and the contact angle of air bubbles in the water outside the track is 100°. The arrangement spacing of each superhydrophobic track structure 2 arranged side by side at equal intervals is 4.2 mm. Thus, a series of cycloid-shaped conical column array track surfaces capable of efficient underwater drag reduction, that is, an underwater drag reduction structure, is formed.

[0068] Place the underwater drag reduction structure formed in this embodiment in water. By supplying bubbles 4 at the front end of the superhydrophobic track structure 2, the measured gas film thickness formed is 3.2 mm. At the same time, connect a force sensor to the track surface of the superhydrophobic track structure 2 for a drag reduction test experiment. The measured drag reduction rate of this surface at different water flow rates and different gas flow rates is 44.4% - 24.1%. In this embodiment, the force sensor is connected to a preset small boat model, and a drag reduction sheet with this underwater drag reduction structure is loaded at the bottom of the small boat model to conduct a drag reduction test experiment. The connection method and test method for the drag reduction test experiment through the force sensor are both well-known prior art means and will not be elaborated here.

[0069] The comparative examples of this embodiment are as follows:

[0070] Comparative Example 1:

[0071] An ordinary aluminum surface without a microarray structure. After removing the surface oxide film, its surface is not subjected to low surface energy modification, as Figure 4 shown. Place the ordinary aluminum surface without a microarray structure in water and supply bubbles at the front end of the ordinary aluminum surface without a microarray structure. At this time, this surface can only capture some discrete bubbles C and cannot form a stable gas film D.

[0072] Comparative Example 2:

[0073] A superhydrophobic aluminum surface without a microarray structure, after removing the surface oxide film, uses a low surface energy modification technique to treat its surface to obtain an aluminum surface with superhydrophobic properties. As Figure 8 shown, the contact angle of water droplets in the air on this surface is 57°, and the contact angle of air bubbles in water on this surface is 90°; as Figure 5 shown, placing this superhydrophobic aluminum surface without a microarray structure in water and supplying air bubbles at its front end, at this time this surface can capture air bubbles and form an air film E, and after shooting with a high-speed camera, the thickness of the air film is further measured to be 1.2 mm. The method of obtaining the air film thickness by shooting pictures with a high-speed camera is a well-known technical means in the prior art and will not be elaborated here;

[0074] It can be known through comparative examples that: the air film formed by the stable thick air film underwater drag reduction structure based on the spontaneous and rapid transportation of air bubbles in this embodiment has higher stability and can maintain a higher air film thickness.

[0075] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A stable thick gas film underwater drag reduction structure based on spontaneous and rapid bubble transportation, characterized in that, It includes a superhydrophobic track structure (2) that is arranged side by side at equal intervals on a substrate (1) and is used to form an underwater drag-reducing air film. The superhydrophobic track structure (2) includes a first track segment (21) and a second track segment (22). Moreover, the outer contour of the first track segment (21) is an arc-symmetric structure that contracts from one end to the other end, and a cone-column array (4) is provided on the upper surface of the first track segment (21) for retaining air bubbles underwater. One end of the second track segment (22) is connected to one end of the first track segment (21), and the second track segment (22) includes a plurality of cone-column array track segments (3) with a cycloid contour structure (222) at the edges arranged in series for air bubble transmission. Moreover, a transition arc contraction section (221) for driving the air bubble flow between the first track segment (21) and the second track segment (22) or between adjacent cone-column array track segments (3) is provided between the connection end of the first track segment (21) and the second track segment (22) and between each cone-column array track segment (3). The cone-column array (4) provided on the upper surface of the cone-column array track segment (3) is used to capture the flowing air bubbles and spread them to form an air film over the entire track.

2. The stable thick gas film underwater drag reduction structure based on spontaneous and rapid bubble transportation according to claim 1, wherein The transition arc radius of the transition arc contraction section (221) is 1 mm. Moreover, one end of the transition arc contraction section (221) is connected to one end of the second track segment (22), the other end of the transition arc contraction section (221) is connected to one end of the first track segment (21), or both ends of the transition arc contraction section (221) are respectively connected to one end of adjacent cone-column array track segments (3).

3. The stable thick air film underwater drag reduction structure based on spontaneous rapid transportation of bubbles according to claim 2, characterized in that The bottom radii of the cones in the cone-column array (4) provided on the cone-column array track segment (3) and the first track segment (21) are both 100 - 300 μm. The height of the cones is 350 - 450 μm. The center distance between each cone is 400 - 600 μm. The bottom surface of the cone-column array (4) is 400 - 500 μm away from the upper surface of the substrate (1).

4. A stable thick gas film underwater drag reduction structure based on spontaneous rapid bubble transportation according to claim 3, characterized in that, The width ratio at both ends of the cycloid contour structure (222) is equal to 0.

8. The cycloid length is 21 - 23 mm.

5. The stable thick air film underwater drag reduction structure based on spontaneous rapid transportation of bubbles according to claim 1, wherein, The spacing of the superhydrophobic track structure (2) on the substrate (1) is 4 - 4.5 mm.

6. A forming method of a stable thick gas film underwater drag reduction structure based on spontaneous rapid transportation of bubbles according to any one of claims 1 to 5, characterized in that, Specifically, it includes the following steps: S1: Cover a layer of black polyethylene film on the substrate (1) to obtain a combined substrate (1). S2: Based on laser processing technology, according to the edge contour shape of the superhydrophobic track structure (2), perform a primary scanning process on the combined substrate (1) to obtain a primary processed substrate (1). And remove the black polyethylene film surrounded by the edge contour shape on the primary processed substrate (1). S3: Again adopt laser processing technology to perform a scanning process on the substrate obtained in S2 for the cone-column array (4) structure to obtain a secondary processed substrate (1). Moreover, the laser parameters of the secondary processed substrate (1) are the same as those of the primary scanning process. S4: Immerse the secondary processed substrate (1) in a fluorosilane solution for soaking, put the soaked secondary processed substrate (1) into an oven for drying, and finally remove the remaining black polyethylene film, thereby obtaining the superhydrophobic track structure (2) for forming an underwater drag-reducing air film.

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