Monomer structure and resistance reduction structure

Abstract

The invention discloses a monomer structure and a resistance reduction structure. The monomer structure comprises a monomer structure base body and a groove structure on the monomer structure base body. In the extending direction of the groove structure, the depth of the groove structure is gradually reduced from the center to the two sides, the flow speed of the center area is high, the deep groove can reduce the direct contact area of fluid and the surface of the base body, and friction resistance is reduced; the flow velocity on the two sides is low, the shallow grooves can avoid formation of retention eddy current, local energy loss is reduced, and resistance reduction uniformity in the flowing direction is achieved; the depth of the grooves is gradually reduced from the central groove to the grooves on the two sides in parallel to the extending direction of the groove structure, the central groove plays a main role in diversion, and the deep design can strengthen the'groove effect '; the grooves on the two sides assist in shunting, fluid channeling between the adjacent grooves can be avoided through the shallow design, and the overall flowing stability is improved. The trench structure is optionally a continuous structure or a discontinuous structure.

Description

Technical Field

[0001] This invention relates to the field of fluid drag reduction, specifically to a single-unit structure and a drag reduction structure. Background Technology

[0002] With the widespread use of high-speed vehicles such as airplanes and high-speed trains, the benefits of drag reduction design in reducing operating energy consumption are becoming increasingly significant. As a result, fluid drag reduction technology has become a research focus in academia and industry, and various implementation methods have emerged.

[0003] Yang Hongwei et al. from Beijing University of Aeronautics and Astronautics proposed a rhomboid mesh circular pit lattice structure, while Pan Jiazheng from Nanjing University of Aeronautics and Astronautics proposed a spaced small rib structure perpendicular to the fluid direction. Both are based on the concept of inducing and controlling the arrangement of surface vortices to reduce drag. Since the 1980s, research institutions represented by NASA have adopted a parallel groove group structure similar to "sharkskin" to reduce drag by suppressing surface vortices perpendicular to the flow direction, but its effect on raising low-speed strip vortices is limited.

[0004] The two existing drag reduction structures have significant design differences and rely on different core fluid dynamics principles, making it difficult to achieve a balanced drag reduction effect and meet the requirements for better drag reduction. There is an urgent need for a new structure that can integrate multiple fluid dynamics drag reduction principles. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a single-unit structure and a drag-reducing structure.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a single-unit structure, comprising a single-unit structure substrate and a groove structure on the single-unit structure substrate; along the extension direction of the groove structure, the depth of the groove structure gradually decreases from the center to both sides, and is parallel to the extension direction of the groove structure. From the central groove to the two side grooves, the groove depth gradually decreases. The groove structure can optionally be a continuous structure or a discontinuous structure. The flow velocity in the central region is high, and the deeper grooves can reduce the direct contact area between the fluid and the substrate surface, thereby reducing frictional resistance. The flow velocity on both sides is low, and the shallower grooves can avoid the formation of stagnant eddies, reduce local energy loss, and achieve drag reduction uniformity along the flow direction.

[0007] Preferably, the top width of the trench structure is 2um-400um.

[0008] Preferably, the maximum depth H of the trench structure is 2um-500um, and the upper limit of the maximum depth H does not exceed 90% of the thickness of the monolithic structure substrate. The method of forming the trench structure on the monolithic structure substrate includes directly creating the trench structure on the surface of the monolithic structure substrate by laser processing. If the depth exceeds 90%, the remaining wall thickness of the monolithic structure substrate is too thin, and it is easy to bend and deform or even break under the action of fluid pressure. The upper limit of 90% can ensure that the remaining wall thickness of the substrate can withstand the conventional fluid pressure. In addition, this depth range can also adapt to the fluid pressure requirements of different application scenarios.

[0009] Preferably, the length of the single-unit structure is 20um-20mm, and the area ranges from 40um² to 400mm².

[0010] Preferably, the spacing between different groove structures within the single structure is adjustable, with a spacing range of 200nm-20mm.

[0011] Preferably, when the trench structure is a discontinuous structure, the spacing between the trench structures is 150nm-6000nm.

[0012] It also protects a drag-reducing structure comprising at least two of the above-mentioned monomer structures.

[0013] Preferably, the drag-reducing structure is formed by overlapping and intersecting different individual structural parts, and the overlapping part does not exceed 65% of the projected area of ​​one of the individual structural parts. This ensures that the core groove area of ​​each individual part, such as the groove section with the largest central depth, is not blocked. This achieves cross-flow guidance without affecting the drag-reducing function of the individual part. By adjusting the overlap angle of the individual parts, the groove structure can smoothly transition with the curvature change, avoiding fluid boundary layer separation caused by abrupt changes in the curvature. The overlap ratio of ≤65% can avoid surface unevenness caused by excessive thickness of the overlapping area and reduce turbulence interference of the fluid at the protrusion.

[0014] Preferably, when the geometric center deviation of the two drag-reducing units does not exceed 50% of the maximum size of the drag-reducing unit along the extension direction of the groove structure, the overlap is perpendicular to the direction of the groove structure; when the geometric center deviation of the two drag-reducing units exceeds 50% of the maximum size of the drag-reducing unit, the overlap is along the direction of the groove structure. From the perspective of flow control, the overlap perpendicular to the groove direction is suitable for local high drag areas, such as the wingtip of an aircraft. The cross-arranged grooves can form a "grid" flow guiding structure, which can reduce local drag by 10%-20%.

[0015] Preferably, the drag reduction structure is formed by the independent combination of different individual structures. The independent combination includes sequential arrangement or cross arrangement, and the spacing between the individual structures is 0-5000um, calculated based on the minimum edge distance between the structures.

[0016] Preferably, in the sequentially arranged drag-reducing monomers, the line connecting the geometric centers of adjacent drag-reducing monomers is parallel to the extension direction of the trench structure.

[0017] Preferably, the trench structure is a discontinuous trench, and L is the maximum spacing along the parallel lines of two discontinuous trenches.

[0018] Compared with the prior art, the beneficial effects of the present invention are: 1. The single-unit structure of the present invention adopts a dual gradient design of groove depth, which is lowered from the center to both sides along the extension direction and the parallel extension direction. This can guide the fluid to flow smoothly, reduce wall friction and eddy current generation, and significantly improve the drag reduction rate compared with traditional equal-depth grooves.

[0019] 2. Multiple units can be combined by overlapping or independently to form a drag-reducing structure, which is suitable for unidirectional and multidirectional flow fields and complex carrier surfaces, making it highly versatile. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the monomer structure of the present invention; Figure 2 This is a schematic diagram of the discontinuous trench structure within the monolithic structure of the present invention; Figure 3 This is a schematic diagram of the monomer structure arrangement of the present invention; Figure 4 This is a schematic diagram of the overlapping arrangement of the monomer structures of the present invention; Figure 5 This is a schematic diagram of an actual processed sample of the drag reduction structure of the present invention.

[0021] In the figure: 1. Monolithic structural matrix; 2. Monolithic internal groove structure. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Please see the appendix Figure 1A monolithic structure includes a monolithic matrix and groove structures on the matrix. Along the extension direction of the groove structures, the depth gradually decreases from the center to both sides. The central region has a high flow velocity, and the deeper grooves reduce the direct contact area between the fluid and the matrix surface, lowering frictional resistance. The sides have lower flow velocities, and the shallower grooves prevent the formation of stagnant eddies, reducing local energy loss and achieving uniform drag reduction along the flow direction. Parallel to the extension direction of the groove structures, the groove depth gradually decreases from the central groove to the side grooves. The central groove plays a major guiding role, and its deeper design enhances the "groove effect." The side grooves assist in flow diversion, and their shallower design prevents fluid cross-flow between adjacent grooves, improving overall flow stability. The groove structures can be either continuous or discontinuous, broadening application scenarios. Continuous structures are suitable for high-velocity, low-viscosity fluids, forming complete flow channels and preventing fluid leakage.

[0024] Please continue to refer to the appendix. Figure 1 The width of the trench structure is S; more specifically, S is defined as the width at the point where the slope abruptly changes at the top of the trench structure. (See attached...) Figure 1 In the diagram, S represents the maximum width of the top of the trench structure. (See attached diagram.) Figure 1 In the middle, the left figure is a top view of the single structure, the upper right figure is a schematic diagram of the maximum depth section parallel to the direction of a single trench structure, and the lower right figure is a schematic diagram of the maximum depth section perpendicular to the direction of the trench.

[0025] In some implementations, the top width S of the trench structure is in the range of 2um-400um. After multiple tests, it was found that when the top width of the trench structure is less than 2um, the trench is prone to blockage due to the surface tension of the fluid, which will increase the flow resistance. At the same time, when the width is greater than 400um, secondary turbulence is easily formed in the trench, that is, the fluid generates local vortices in the trench, which destroys the stable laminar boundary layer and reduces the drag reduction efficiency.

[0026] Please see the appendix Figure 2 The trench structure can also be a discontinuous structure. A discontinuous trench structure, also along its extension direction, has a depth that gradually decreases from the center to the sides. (Attached) Figure 2 In the middle, the left figure is a top view of the single structure, the upper right figure is a schematic diagram of the maximum depth section parallel to the direction of a single trench structure, and the lower right figure is a schematic diagram of the maximum depth section perpendicular to the direction of the trench.

[0027] In some implementations, the maximum depth H of the trench structure is 2µm-500µm. Similar to the top width of the trench structure, the maximum depth was determined through numerous experiments. When the depth is less than 2µm, an effective fluid isolation layer cannot be formed; when the depth is greater than 500µm, although the drag reduction rate can be improved, it leads to increased fluid shear force on the trench wall, thus increasing local energy consumption. A depth range of 2µm-500µm allows the drag reduction rate to be stabilized at 10%-30%, while avoiding energy loss due to excessive depth.

[0028] In the above embodiments, the maximum depth H of the groove structure does not exceed 90% of the thickness of the monolithic structure substrate. The method of forming the groove structure on the monolithic structure substrate includes directly creating the groove structure on the surface of the monolithic structure substrate by laser processing. If the depth exceeds 90%, the remaining wall thickness of the monolithic structure substrate is too thin, and it is easy to bend and deform or even break under the action of fluid pressure. The upper limit of 90% can ensure that the remaining wall thickness of the substrate can withstand the conventional fluid pressure. In addition, this depth range can also adapt to the fluid pressure requirements of different application scenarios.

[0029] In some implementations, the individual structural dimensions are 20um-20mm in length and 40um²-400mm² in area.

[0030] In some implementations, the spacing between different trench structures within the monolithic structure is adjustable, ranging from 200nm to 20mm.

[0031] In some implementations, when the trench structure is discontinuous, the spacing between the trenches ranges from 150nm to 6000nm. This flexible adjustment of the spacing allows for precise adaptation to different fluid characteristics and application scenarios, solving the problem of fixed trench spacing and narrow applicability. The trench spacing directly affects the flow state of the fluid between the trenches: for low-viscosity fluids, such as air, a smaller spacing of 150nm-1000nm can be selected, forming a thicker laminar boundary layer through dense trenches, reducing turbulence interference and improving drag reduction efficiency; for high-viscosity fluids, such as crude oil, a larger spacing of 1000nm-6000nm can be selected to avoid increased resistance caused by high-viscosity fluid stagnation within narrow spacing, ensuring smooth fluid flow.

[0032] This application also protects a drag-reducing structure comprising at least two of the above-mentioned monomer structures.

[0033] Please see the appendix Figure 3 In the left image, multiple units are arranged in sequence; regardless of the horizontal or vertical perspective, all units maintain a consistent sequential arrangement. In the right image, multiple units are arranged in a crisscross pattern; from the vertical perspective, the units still maintain a sequential arrangement; however, when switching to the horizontal perspective, the units are staggered.

[0034] Please see the appendix Figure 4 In some implementations, the drag-reducing structure is formed by overlapping and intersecting different individual structural components. From the perspective of structural synergy, the core purpose of this overlapping and intersecting is to form a more complex flow-guiding network through the complementary grooves between the individual components. Furthermore, the overlapping portion does not exceed 65% of the projected area of ​​any one of the individual structural components, ensuring that the core groove area of ​​each component, such as the groove segment with the greatest central depth, is not obstructed. This achieves cross-flow guidance without affecting the drag-reducing function of a single component. By adjusting the overlap angle of the components, the groove structure can smoothly transition with changes in curvature, avoiding fluid boundary layer separation caused by abrupt changes in surface curvature. A ≤65% overlap ratio avoids surface unevenness caused by excessively thick overlapping areas, reducing turbulent interference at protrusions.

[0035] In some implementations, when the geometric center deviation of the two drag-reducing units does not exceed 50% of the maximum size of the drag-reducing unit along the extension direction of the trench structure, the overlap is perpendicular to the direction of the trench structure; when the geometric center deviation of the two drag-reducing units exceeds 50% of the maximum size of the drag-reducing unit, the overlap is along the direction of the trench structure. Overlapping along the trench direction is suitable for long straight surfaces, such as long-distance pipelines and the sides of high-speed train vehicles, which can extend the effective length of the trench, so that the fluid can be continuously controlled by the boundary layer over a distance of hundreds of meters or even longer, avoiding the attenuation of drag reduction effect in long-distance flow.

[0036] In some implementations, the drag-reducing structure is formed by independently combining different individual structures. These independent combinations include sequential or crisscrossing arrangements. Sequential arrangements are suitable for linear fluid channels, where continuous grooves along the fluid flow direction can create a unidirectional flow corridor, reducing lateral flow interference. Crosscrossing arrangements are suitable for complex curved surfaces or multi-directional fluid scenarios, where intersecting grooves can cope with fluid impacts from different angles, avoiding a surge in local resistance caused by oblique flow in a single-directional groove. Furthermore, based on the minimum edge distance between structures, the spacing between independently combined individual structures is 0-5000µm. When the spacing is 0µm, the individual structures are tightly joined to form a complete drag-reducing surface, suitable for scenarios with extremely high drag-reduction efficiency requirements. When the spacing is 1000-5000µm, the number of individual structures used can be reduced while ensuring basic drag-reduction effects.

[0037] A method for fabricating a drag-reducing structure employs a laser processing device, which includes an optical system. The optical system's light source has a wavelength range of 200-20000 nm and can form a periodic spatial array of light spots, with the spot structure being strip-shaped or rhomboid. The processing method includes: the optical system forming a groove structure on a single structural substrate, with the depth of the groove structure gradually decreasing from the center to both sides along its extension direction; and fabricating multiple groove structures in parallel along the extension direction of the groove structure, with the depth gradually decreasing from the central groove to the side grooves. The central groove plays a major role in guiding flow, and its deeper design enhances the groove effect; the side grooves assist in flow diversion, and their shallower design prevents fluid cross-flow between adjacent grooves, improving overall flow stability. Simultaneously, the groove structure can be optionally continuous or discontinuous, broadening the application scenarios. Continuous structures are suitable for high-velocity, low-viscosity fluids, forming complete flow channels and preventing fluid leakage.

[0038] In some implementations, the optical system can be equipped with at least two light sources of different wavelengths simultaneously. The 200-400nm ultraviolet light source is used to process fine grooves requiring a precision of ≥100nm. Its core advantage lies in its extremely short wavelength and small focused spot size, enabling precise processing of fine grooves with a precision requirement of ≥100nm. The 760-20000nm infrared light source is used to process monolithic structural substrates or high-hardness carriers with a thickness of ≥380nm. Leveraging its high energy density, it is suitable for monolithic structural substrates or high-hardness carriers with a thickness of ≥100µm, including metals, composite materials, and ceramics. These materials are either thick or have high hardness, making it difficult for traditional low-energy light sources to form effective groove depths. The 400-760nm green light source is used to process flexible polymer film substrates. For flexible polymer film substrates, such as polyimide, polyetheretherketone films, metals, composite materials, and ceramics, its moderate energy density avoids the problems of low processing efficiency of ultraviolet light sources and low absorption rate and large thermal impact of infrared light sources.

[0039] In some implementations, the spacing of the array structures within a single spot in the periodic spatial array structure formed by the optical system can be adjusted within the range of 50µm-800µm. This allows the arrangement density of the groove structures to be flexibly adjusted according to drag reduction requirements, avoiding the mismatch between the structure and the flow field caused by a fixed spacing. Furthermore, the array spacing is adapted to the spacing of the groove structures within the single structure. When the grooves within the single structure are closely packed, the array spacing is set to 1µm-300µm to match the half-width at half-maximum of the sinusoidal convex structure. This enables adjacent grooves to form a continuous wavy surface, allowing the fluid to smoothly transition along the convex contour when flowing through, reducing the generation of eddies between grooves. When the grooves are not closely packed, the array spacing approximates a boss structure. The interval between the bosses can form a stable fluid channel, enhancing the structure's guiding effect on the fluid and avoiding the drag superposition that may result from close packing.

[0040] In some implementations, the single-spot energy of the optical system is continuously adjustable, with the energy adjustment range adapted to the processing object. When processing polymer films, the single-spot energy is set to 10μJ-100mJ to avoid film burn-through, ensuring smooth trench sidewalls and a intact film substrate. This allows the flexible drag-reducing structure to maintain its designed fluid disturbance suppression function while preserving the film's mechanical properties. When processing metal or ceramic carriers, the single-spot energy is set to 100μJ-2mJ to ensure trench depths reach 2-500µm, with the maximum depth not exceeding 90% of the carrier thickness. This avoids a decrease in carrier strength or structural damage due to excessively deep trenches, ensuring the mechanical stability of the drag-reducing structure on rigid carriers. From the perspective of energy control in structural processing, precise control of trench depth and effective protection of the substrate structure are achieved, enabling the drag-reducing structure to maintain its designed function and structural integrity on carriers of different materials, thus improving application reliability.

[0041] In some implementations, the optical system has a focus tracking function that follows the surface undulations of the object being processed, with a tracking accuracy of <±2mm. When processing curved carriers, the focus position of the optical system is adjusted by detecting the height of the surface undulations in real time, ensuring that the groove depth deviation in different areas is ≤5%, thus avoiding the failure of the drag reduction structure due to surface undulations. When processing curved carriers, traditional laser processing is prone to excessive groove depth deviation in different areas due to surface undulations. However, the tracking function can ensure that the groove depth deviation is ≤5% by detecting surface undulations in real time and adjusting the focus position. This allows the drag reduction structure on the curved carrier to act uniformly on the fluid flowing over the curved surface, avoiding turbulent flow caused by excessively deep or shallow grooves. Excessively deep areas may form eddies, while excessively shallow areas cannot effectively guide laminar flow.

[0042] In some embodiments, the laser processing method includes: firstly, fabricating drag-reducing monomer structures or combined structures on a polymer film using an optical system, and then attaching the polymer film to the surface of the carrier to be drag-reduced. This achieves high-precision fabrication of the drag-reducing structure and ensures its long-term effectiveness through stable adhesion, making it particularly suitable for complex shapes or flexible carriers. It improves the drag-reduction effect in terms of structural precision and durability. The optical system uses a 200-400nm deep ultraviolet light source to form a strip array of light spots. Before laser processing, the surface of the polymer film is plasma etched to improve the light spot absorption efficiency, and then cured after attachment.

[0043] In some embodiments, the laser processing method includes: directly fabricating a drag-reducing structure on the surface of the carrier to be drag-reduced using an optical system; the optical system uses a 760-20000nm infrared light source to form a rhomboid array of light spots, and the laser processing parameters meet the following requirements: wavelength 1064nm-10.6um, power 100W-1500W, and processing speed 100mm / s-5000mm / s. Inert gas can also be introduced during processing to protect the processing area. Inert gas protection during processing prevents oxidation or impurity formation in metal, ceramic, and other carriers during high-temperature processing, ensuring a smooth groove surface and reducing frictional resistance during fluid flow. This direct processing method integrates the drag-reducing structure with the carrier, improving the mechanical stability of the structure. The structure formed by the rhomboid light spots enhances adaptability to complex flow fields, improving drag reduction efficiency in terms of structural integrity and anti-interference capabilities.

[0044] The principle of this invention is as follows: The single-unit structure has a groove structure, and the combined structure of the single units has a continuous groove structure. The groove structure can suppress the generation of transverse vortices perpendicular to the direction of the groove structure, thereby playing a drag reduction function similar to a "sharkskin" structure. At the same time, the single-unit structure of this invention has a groove structure depth variation, and the combined structure of multiple single-unit structures has a periodic groove structure depth variation or a periodic groove structure and non-groove structure variation. This periodic depth variation can guide the fluid into the groove structure, further restricting the transverse vortices. Meanwhile, the raised part of the groove structure can guide the upward airflow along the wall to rise away from the wall surface, forming vortices on the far wall surface, further reducing the fluid resistance of the thin surface.

[0045] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A single-unit structure, characterized in that, It includes a single structural substrate and a groove structure on the single structural substrate; along the extension direction of the groove structure, the depth of the groove structure gradually decreases from the center to both sides, and parallel to the extension direction of the groove structure, the groove depth gradually decreases from the central groove to the side grooves, and the groove structure can optionally be a continuous structure or a discontinuous structure.

2. The monolithic structure according to claim 1, characterized in that, The top width of the trench structure is 2um-400um.

3. The monolithic structure according to claim 1, characterized in that, The maximum depth H of the trench structure is 2um-500um, and the upper limit of the maximum depth H does not exceed 90% of the thickness of the substrate of the monolithic structure.

4. The monolithic structure according to claim 1, characterized in that, The dimensions of the single-unit structure are 20um-20mm in length and 40um²-400mm² in area.

5. The monolithic structure according to claim 1, characterized in that, The spacing between different groove structures within the single-unit structure is adjustable, ranging from 200nm to 20mm.

6. The monolithic structure according to claim 1, characterized in that, When the trench structure is a discontinuous structure, the spacing between the trench structures is 150nm-6000nm.

7. A drag-reducing structure, characterized in that, It includes at least two monomeric structures as described in any one of claims 1-6.

8. The drag reduction structure according to claim 7, characterized in that, The drag-reducing structure is formed by overlapping and intersecting different individual structural parts, and the overlapping part of the overlapping and intersecting part does not exceed 65% of the projected area of ​​one of the individual structural parts.

9. The drag-reducing structure according to claim 7, characterized in that, When the geometric center deviation of the two drag-reducing units does not exceed 50% of the maximum size of the drag-reducing unit along the extension direction of the groove structure, the overlap is an overlap perpendicular to the direction of the groove structure; when the geometric center deviation of the two drag-reducing units exceeds 50% of the maximum size of the drag-reducing unit, the overlap is an overlap along the direction of the groove structure.

10. The drag-reducing structure according to claim 7, characterized in that, The drag-reducing structure is formed by the independent combination of different individual structures. The independent combination includes sequential arrangement or cross arrangement, and the distance between the individual structures is calculated based on the minimum edge distance between the structures. The distance between the individual structures in the independent combination is 0-5000um.

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