A drag-reducing airfoil-shaped hanger ring and wide-speed-range AUV

Abstract

The application provides a drag-reducing airfoil-shaped lifting ring and a wide-speed-range AUV, wherein the drag-reducing airfoil-shaped lifting ring comprises a lifting ring body, the airfoil shape of the lifting ring body is a NACA symmetrical airfoil, and the lifting ring body comprises two axis-symmetrical first airfoil-shaped lifting rings and second airfoil-shaped lifting rings; wherein the two sides of the first airfoil-shaped lifting ring and the second airfoil-shaped lifting ring away from each other are convex arc curved surfaces, the convex directions of the two arc curved surfaces are opposite, and lifting holes for lifting an autonomous underwater vehicle (AUV) are arranged at the convex positions of the first airfoil-shaped lifting ring and the second airfoil-shaped lifting ring. The drag-reducing airfoil-shaped lifting ring can realize the functions of reducing drag and reducing energy consumption, and the voyage of the AUV is improved.

Description

Technical Field

[0001] This application relates to the field of underwater vehicle launching, and more particularly to a drag-reducing airfoil lifting ring and a wide-speed-range AUV. Background Technology

[0002] An Autonomous Underwater Vehicle (AUV) is an unmanned vehicle capable of autonomous or remotely controlled navigation underwater. Characterized by its high stealth capabilities and wide maneuverability, it is widely used in both civilian and military fields. For example, it can be used for tasks such as seabed exploration, marine scientific research, and underwater rescue, as well as reconnaissance, mine countermeasures, and intelligence gathering.

[0003] To significantly expand the operational range and efficiency of autonomous underwater vehicles (AUVs) and meet their continuous operational needs in various mission scenarios such as wide-area seabed topographic exploration, water quality monitoring, information gathering, and emergency rescue, regular AUV refueling is crucial. Adding lifting rings to the AUV body is an effective means of achieving rapid deployment and recovery operations.

[0004] However, for wide-speed-range AUVs (3 knots to 50 knots), traditional ring structures introduce significant additional drag during navigation. Especially at high speeds, this drag, primarily pressure drag, increases dramatically, significantly raising the overall drag of the AUV, increasing energy consumption, and potentially leading to a significant increase in flow noise levels, adversely affecting tasks such as acoustic detection. Summary of the Invention

[0005] To address the issue of increased drag in AUVs due to the addition of airlocks, embodiments of this application provide a drag-reducing airfoil airlock and a wide-speed-range AUV. This drag-reducing airfoil airlock design can reduce drag and energy consumption, thereby increasing the range of the AUV.

[0006] Therefore, the following technical solutions are adopted in the embodiments of this application:

[0007] In a first aspect, a drag-reducing airfoil lifting ring includes: a lifting ring body, wherein the airfoil of the lifting ring body is a NACA symmetrical airfoil, and the lifting ring body includes two axisymmetric first airfoil lifting rings and second airfoil lifting rings; wherein the two mutually distant sides of the first airfoil lifting rings and the second airfoil lifting rings are convex arcuate surfaces, the two arcuate surfaces protrude in opposite directions, and lifting holes for lifting autonomous underwater vehicles (AUVs) are provided at the protrusions of the first airfoil lifting rings and the second airfoil lifting rings.

[0008] In this embodiment, the lifting ring body is axially symmetrically composed of a "first airfoil lifting ring" and a "second airfoil lifting ring," with the two curved surfaces protruding in opposite directions. This symmetrical structure ensures a uniform flow field distribution when water flows over both sides of the lifting ring, preventing localized velocity anomalies and uneven drag caused by a single-sided protrusion, thus balancing the flow field. Whether the AUV is operating at low speeds (3 knots) or high speeds (50 knots), the symmetrical layout keeps the airfoil within an optimal angle of attack range, maintaining low drag characteristics (avoiding excessive airfoil angles of attack due to velocity changes, which could trigger flow separation), making it suitable for wide-speed-range AUVs. Lifting holes are created at the airfoil protrusions, ensuring that the hole positions blend with the airfoil surface and do not create new "flow obstruction points," thus ensuring that the drag reduction design does not affect the core functions of lifting, launching, and recovering.

[0009] Furthermore, the airfoil profile utilizes the mature and reliable NACA (National Advisory Committee for Aeronautics) series of symmetrical airfoils. This airfoil is supported by a wealth of publicly available hydrodynamic databases and has been validated through extensive engineering practice. Its low-drag characteristics effectively improve the flow structure around the AUV shell and lifting rings, significantly suppressing flow separation, thereby reducing flight drag and propulsion energy consumption, and effectively minimizing flow-induced noise.

[0010] As one feasible implementation, the first and second airfoil rings can be detachably mounted on the autonomous underwater vehicle (AUV) after they are engaged with each other.

[0011] In this embodiment, the first and second airfoil lifting rings are designed to "interlock," meaning their curved surfaces can be joined to form a complete symmetrical airfoil profile. The resulting integrated airfoil profile perfectly conforms to the streamlined characteristics of the NACA symmetrical airfoil, ensuring smooth water flow along the smooth surface and maximizing its core advantages of low drag and noise reduction. Furthermore, the interlocking design creates an "interlocking" assembly between the two lifting ring modules, enhancing the overall structural stability and preventing deformation or displacement of individual rings under water flow impact. During installation, the interlocked double-airfoil lifting rings are aligned with the pre-set mounting position on the AUV housing (e.g., the original lifting ring location) and quickly secured using fasteners or clips, eliminating the need for complex welding or permanent bonding. For disassembly, simply loosen the fasteners or release the clips to easily detach the lifting rings from the AUV. In this way, the two airfoils are joined together to form a complete streamlined airfoil, ensuring that the flow state of the water on the surface of the lifting ring is completely consistent with that of the "integrated airfoil lifting ring". The flow field will not be disrupted by the split structure. It retains all the advantages of airfoil drag reduction (low drag, noise suppression, and wide speed range adaptability) and improves the assembly flexibility through modular and detachable design.

[0012] In one feasible implementation, the first airfoil and the second airfoil are connected to each other by fastening bolts.

[0013] In this embodiment, bolt tightening ensures a tight fit between the two first and second airfoil lifting rings, with no gaps or misalignments at the mating surfaces. This prevents water from seeping in through gaps or creating eddies at misalignments, ensuring the streamlined characteristics of the overall airfoil and fundamentally preserving its core functions of drag reduction and noise suppression. The tightening bolts provide a stable axial preload, firmly locking the two lifting rings together to form a rigid whole. This rigid structure can withstand the impact of high-speed water flow (such as hydrodynamic loads under 50kN conditions) and the pulling force during lifting and retrieval (such as the weight load when an AUV is lifted), preventing the clamping structure from loosening or deforming.

[0014] As one feasible implementation, the first airfoil lifting ring has a countersunk through hole; the second airfoil lifting ring has a threaded hole; wherein the axis of the countersunk through hole and the threaded hole coincide.

[0015] In this embodiment, the bolt head is fully recessed into the countersunk hole, and the outer surface of the first airfoil remains smooth, perfectly blending with the streamlined contour of the NACA symmetrical airfoil. This avoids introducing additional "bolt resistance," resulting in superior drag reduction compared to a conventional through-hole and nut connection method (where the nut may protrude). Furthermore, the bolt only needs to be inserted and tightened unidirectionally from the first airfoil side, eliminating the need for operations on the second airfoil side (such as installing a nut). This is particularly suitable for scenarios where the gap between the AUV housing and the airfoil is narrow, significantly reducing assembly difficulty and shortening installation time.

[0016] In one feasible implementation, the first or second airfoil lifting ring includes a leading edge side, a mid-section side, a rear section side, and a tail end side; wherein, along a first direction, from the leading edge side to the mid-section side, the projected thickness of the first or second airfoil lifting ring along a second direction gradually increases; along the first direction, from the rear section side to the tail end side, the projected thickness of the first or second airfoil lifting ring along the second direction gradually decreases; the length of the mid-section side is less than the length of the rear section side; the first direction is the forward direction of the AUV, and the second direction is perpendicular to the first direction.

[0017] In this embodiment, the smooth thickness gradient (without abrupt changes or sharp edges) allows the water flow to adhere to the surface of the lifting ring throughout its entire trajectory. Although the frictional area between the water flow and the surface is not reduced, the flow state is more stable, and the frictional resistance coefficient (C) is lower. fThe thickness is significantly lower, especially under low-speed conditions (3-10 knots). The thickness distribution from the leading edge to the trailing edge minimizes the pressure difference between the front and rear of the lifting ring. For example, the transition between the high-pressure zone at the maximum thickness in the middle section and the low-pressure zone at the trailing edge is smooth, avoiding the formation of a strong pressure difference environment of "high pressure at the front and low pressure at the back" (the main source of resistance in traditional irregular lifting rings). Under high-speed conditions (10-50 knots), it can effectively suppress the sharp increase in resistance. The gradual thickness allows the water flow to be orderly throughout the "diversion-flow-convergence" process, with almost no eddy currents generated, reducing flow-induced noise from the source. It is especially suitable for scenarios such as military reconnaissance (concealment requirements) and marine scientific research (high-precision acoustic detection requirements). The connection between the middle and rear sections, as the maximum thickness, is not only a stable flow field zone but also the core structural stress area of ​​the lifting ring. The thickened design can increase the amount of material used in this area, improving the lifting ring's resistance to water flow impact (high-speed conditions) and lifting tension (recovery stage), avoiding sacrificing structural reliability in pursuit of thinning.

[0018] As one feasible implementation, the ends of the leading edge and the tail end that are opposite to each other are smooth chamfered, and the angle of attack of the tail end is smaller than the angle of attack of the leading edge.

[0019] In this implementation, the smooth chamfer at the leading edge reduces water flow impact, especially at high speeds (e.g., 30-50 knots). The high velocity and strong impact of the incoming flow significantly reduce "impact drag" (the main source of additional drag from traditional sharp edges), preventing drag from increasing sharply with velocity. The small angle of attack at the tail end, combined with the smooth chamfer, allows the water flow to converge quickly, shortening the length of the wake region (the low-pressure vortex region behind the lifting ring) and further reducing pressure drag. Even at low speeds (3-10 knots), this reduces the interference of the wake on the AUV's hull flow field. The smooth chamfer at the leading edge avoids turbulence generated by water flow impact, while the smooth chamfer at the tail end, combined with the small angle of attack, reduces wake vortices. Turbulence and vortices are the two main sources of flow-induced noise; this design weakens noise at its source, making it particularly suitable for military reconnaissance (requiring concealment) and marine scientific research (requiring high-precision sonar detection).

[0020] As one possible implementation, the leading edge and tail end sides facing away from the AUV are provided with rounded chamfers.

[0021] In this embodiment, the rounded chamfer eliminates the sharp protrusions at the outer edge. When water flows along the rounded surface, the boundary layer (the transition layer between the water flow and the surface of the ring) is more stable, making it less prone to turbulent boundary layer formation and reducing the frictional drag coefficient (C). fThe drag is further reduced, especially at high speeds (e.g., 30-50 km / h), where turbulence has a more significant impact on drag, resulting in a more pronounced optimization effect. The rounded chamfer on the outer edge of the tail shortens the wake region (low-pressure vortex region), reducing the pressure difference before and after the lifting ring. Pressure drag is the main drag source for wide-speed-range AUVs during high-speed navigation, and this design effectively suppresses the sharp increase in drag at high speeds. Sharp edges are prone to generating "vortex shedding noise" (pulse noise formed by the periodic detachment of water flow from the edge). The rounded chamfer allows the water flow to move smoothly along the edge, preventing vortex shedding and reducing this type of high-frequency noise at the source, thus reducing interference with AUV sonar detection and underwater communication.

[0022] As one possible implementation, the lifting hole is located at the connection between the middle section side and the rear section side.

[0023] In this embodiment, the lifting hole is located in a low-disturbance flow field region. When water flows through this region, the presence of the lifting hole causes only minor local disturbances and does not trigger large-scale turbulence or eddies. Compared to the design where the lifting hole is located at the leading edge / tail end, the increase in drag can be reduced by more than 60%, completely without affecting the core drag reduction requirements of a wide-speed-range AUV. The airfoil integrity is not compromised: the position of the opening at the mid-section-tail section connection does not alter the overall streamlined profile of the airfoil, which is thickened from the leading edge to the mid-section and thinned from the tail end. This ensures that the airfoil's guiding effect on the water flow is unaffected, and the low-drag characteristics (especially pressure drag control under high-speed conditions) are fully preserved.

[0024] As an achievable implementation, the connection between the leading edge side and the tail end side is a smooth connection, and the leading edge side, the middle section side, the rear section side and the tail end side are integrally formed.

[0025] In this embodiment, the smooth connection eliminates any "flow obstruction points" (such as sharp edges or steps) on the airfoil surface, allowing water to flow continuously without generating localized eddies at the junctions. The one-piece molded structure has no weak points at the joints, and its overall stiffness and strength are far superior to spliced ​​structures. It can withstand greater water flow impact loads (during high-speed navigation) and hoisting impact loads (during recovery and lifting), reducing the risk of structural failure (such as cracking or deformation) by more than 80%.

[0026] Secondly, embodiments of this application also provide a wide-speed-range AUV, including the drag-reducing airfoil lifting ring as described in the first aspect.

[0027] In summary, this application discloses a drag-reducing airfoil lifting ring and a wide-speed-range AUV. The lifting ring structure is designed as an airfoil with a specific hydrodynamic profile. While retaining the convenient recovery function, it significantly improves the flow structure around the vehicle, effectively guides the water flow, suppresses flow separation, reduces pressure drag, and improves the vehicle's endurance. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0029] The various regions, shapes, and their relative sizes and positional relationships shown in the figure are merely illustrative and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0030] In the various figures, the same elements are represented by similar reference numerals. For clarity, the various parts in the figures are not drawn to scale, and certain features may be exaggerated or omitted to more clearly illustrate and explain this application.

[0031] Figure 1 A schematic diagram of the original lifting ring installed on the hull of a traditional autonomous underwater vehicle (AUV) is shown.

[0032] Figure 2 This paper shows a three-dimensional structural schematic diagram of a drag-reducing airfoil lifting ring installed on a wide-speed-range AUV, according to an embodiment of this application.

[0033] Figure 3 A three-dimensional structural schematic diagram of a drag-reducing airfoil lifting ring provided in an embodiment of this application is shown;

[0034] Figure 4 The pressure coefficients on the upper surface of the hull under different speed conditions are shown;

[0035] Figure 5 The pressure coefficient of the upper surface of the hull is shown under the condition of v=15kn;

[0036] Figure 6 The pressure coefficient of the upper surface of the hull is shown under the condition of v=50kn;

[0037] Figure 7 The pressure cloud diagram is shown when the original lifting ring is positioned at the front of the hull;

[0038] Figure 8 The pressure cloud diagram is shown when the airfoil-shaped lifting ring is located at the forward side of the hull;

[0039] Figure 9 The vorticity diagram is shown when the original lifting ring is positioned at the front of the hull.

[0040] Figure 10The vorticity diagram is shown when the airfoil-shaped lifting ring is positioned at the forward side of the hull.

[0041] Figure 11 The vorticity diagram of the original lifting ring at y=0.31 is shown;

[0042] Figure 12 The vorticity diagram of the airfoil lifting ring at y=0.31 is shown.

[0043] In the diagram, 1. Shell; 11. Original lifting ring; 2. Lifting ring body; 21. First airfoil lifting ring; 22. Second airfoil lifting ring; 23. Lifting hole; 24. Fastening bolt; 25. Countersunk through hole; 26. Leading edge side; 27. Middle section side; 28. Rear section side; 29. ​​Tail end side; 3. Smooth chamfer; 4. Rounded chamfer. Detailed Implementation

[0044] The technical solutions in the embodiments of this application will now be described with reference to the accompanying drawings.

[0045] In the description of this application, 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", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application 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, and therefore should not be construed as a limitation of this application.

[0046] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0047] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0048] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0049] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0050] Figure 1 This diagram shows the original lifting ring 11 installed on the hull 1 of a conventional autonomous underwater vehicle (AUV), as shown below. Figure 1 As shown, an original lifting ring 11 is typically installed on the AUV hull 1. The AUV is lifted into the water and retrieved through the cooperation of the hook and the original lifting ring 11. However, the addition of the original lifting ring 11 increases the AUV's drag. Specifically, existing underwater vehicles use conventional original lifting rings 11 (such as cylindrical or simple block structures (see...)). Figure 1 During navigation, it will introduce significant additional drag, mainly manifested as a sharp increase in differential pressure drag dominated by the huge pressure difference formed before and after the lifting ring structure. In addition, conventional lifting ring structures will seriously interfere with the flow field morphology around the vehicle, triggering a series of unfavorable hydrodynamic phenomena such as enhanced turbulence intensity and fluid separation, resulting in adverse consequences such as increased flow-induced noise, induced structural vibration, and additional fluid excitation loads.

[0051] To address this issue, this application proposes and designs a drag-reducing airfoil lifting ring. This innovative design not only retains the inherent ease of deployment and retrieval of the lifting ring, but also incorporates an airfoil configuration based on aerodynamic / fluid dynamic principles, aiming to actively reduce drag. Compared to traditional designs, this airfoil lifting ring effectively reduces drag components during navigation, thereby lowering AUV energy consumption and extending its underwater operating time. Furthermore, adhering to the principles of simple structure, convenient manufacturing, and reliable connection, this design ensures high applicability and widespread value in engineering practice, providing a practical solution to resolving the contradiction between efficient retrieval and low-drag navigation for wide-speed-range AUVs.

[0052] Example

[0053] The technical solutions of the embodiments of this application will be described by way of example below with reference to the accompanying drawings.

[0054] Figure 2 This illustration shows a three-dimensional structural diagram of a drag-reducing airfoil lifting ring installed on a wide-speed-range AUV, as provided in an embodiment of this application. Figure 3 A three-dimensional structural schematic diagram of a drag-reducing airfoil lifting ring provided in an embodiment of this application is shown. Figure 2 and Figure 3 As shown, in this embodiment, two drag-reducing airfoil lifting rings are installed on the shell 1 of the wide-speed-range AUV, with the two airfoil lifting rings located on the front and rear sides of the AUV shell 1, respectively. In one embodiment, the drag-reducing airfoil lifting rings are detachably installed on the original lifting ring 11 on the AUV shell 1, enabling the drag-reducing airfoil lifting rings in this embodiment to improve upon the already welded conventional lifting rings of the autonomous underwater vehicle (AUV). In another embodiment, the drag-reducing airfoil lifting rings can be directly fixed to the AUV shell 1, and the fixing method can be detachable connection or welding to enhance the connection strength between the drag-reducing airfoil lifting rings and the AUV shell 1.

[0055] The structure of the drag-reducing airfoil lifting ring of this application will be described in detail below, taking the case where the drag-reducing airfoil lifting ring is detachably installed on the original lifting ring 11 on the AUV housing 1 as an example.

[0056] For example, the drag-reducing airfoil lifting ring includes: a lifting ring body 2, the airfoil of which is a NACA symmetrical airfoil, and the lifting ring body 2 includes two axisymmetric first airfoil lifting rings 21 and second airfoil lifting rings 22. The two mutually distant sides of the first airfoil lifting rings 21 and the second airfoil lifting rings 22 are convex arcuate surfaces, with opposite convex directions. Lifting holes 23 for launching and lowering autonomous underwater vehicles (AUVs) are provided at the protrusions of the first airfoil lifting rings 21 and the second airfoil lifting rings 22. See reference. Figure 3 , Figure 3The first direction is the navigation direction of the autonomous underwater vehicle (AUV), and the second direction is perpendicular to the first direction. It can be seen that the NACA symmetrical airfoil has a smooth, streamlined profile, with symmetrical upper and lower surfaces, a rounded leading edge, and a sharp trailing edge, which guides water flow smoothly along the airfoil surface. This NACA symmetrical airfoil reduces flow separation; in the low-drag range (e.g., angle of attack ≤ 3°), the water flow can adhere to the airfoil surface throughout, avoiding turbulent eddies caused by separation. Optionally, the NACA symmetrical airfoil can be any one of NACA008, NACA0010, or NACA0012. The embodiments of this application are not limited to these. The above-mentioned NACA symmetrical airfoil models can reduce pressure drag; the pressure difference before and after the airfoil is much smaller than that of traditional structures, and pressure drag is the main source of additional drag on the lifting ring under high-speed conditions (e.g., 50kN).

[0057] Thus, the NACA symmetrical airfoil has a rich public hydrodynamic database and engineering verification cases (such as in the aviation and marine fields), eliminating the need for extensive retesting and reducing design and manufacturing risks. While reducing drag, it retains the core function of the lifting ring for rapid deployment and recovery, and its axisymmetric structure is compatible with the AUV's shell installation, requiring no major modifications to the AUV body and facilitating integration. Traditional lifting ring drag reduction designs often only adapt to a single speed range (e.g., optimizing only low or high speeds), while the NACA symmetrical airfoil has a wider low-drag range (combined with its axisymmetric layout), maintaining a superior flow field across the entire speed range of 3-50 knots, meeting the multi-mission requirements of AUVs that allow for both low-speed operation and high-speed maneuvering. For example, in low-speed conditions (3-10 knots): the airfoil's low-drag characteristics reduce frictional drag, lowering the basic energy consumption of the AUV during low-speed cruise and extending its range. High-speed operation (10-50kN): Suppresses flow separation, significantly reduces pressure drag (the main drag source of traditional airfoils), and avoids a sharp increase in drag with speed, thereby reducing the load on the propulsion system and indirectly improving the high-speed navigation efficiency of the AUV. The turbulent flow field (eddies, separated flows) of traditional airfoils generates significant flow-induced noise, interfering with the acoustic detection (such as sonar) missions of the AUV. Airfoil airfoils, on the other hand, guide the water flow smoothly, reducing eddy generation and reducing flow-induced noise at its source, ensuring the detection accuracy of acoustic equipment, and are particularly suitable for noise-sensitive scenarios such as military reconnaissance and marine scientific research.

[0058] Continue reading Figure 2 and Figure 3In this embodiment, the first airfoil lifting ring 21 and the second airfoil lifting ring 22, after being engaged with each other, are detachably mounted on the shell 1 of the autonomous underwater vehicle (AUV). The curved surfaces of the first airfoil lifting ring 21 and the second airfoil lifting ring 22 can be spliced ​​together to form a complete symmetrical airfoil profile. Optionally, the first airfoil lifting ring 21 and the second airfoil lifting ring 22 are connected by fastening bolts 24. In this embodiment, eight fastening bolts 24 are provided, and the eight fastening bolts 24 are evenly distributed on the circumferential surface (non-frontal surface) of the drag-reducing airfoil lifting ring. It is understood that the mating surfaces (engagement surfaces) of the first airfoil lifting ring 21 and the second airfoil lifting ring 22 will have pre-set bolt holes, and the hole positions and diameters will be perfectly matched. The engagement is achieved through the following steps:

[0059] Positioning and Alignment: Align the curved surfaces of the two airfoil lifting rings in the design direction (opposite protrusion directions) so that the preset bolt holes completely overlap, ensuring that a complete and continuous NACA symmetrical airfoil profile (without misalignment or gaps) is formed after the two rings are joined.

[0060] Bolt tightening: Pass the fastening bolt 24 through the aligned bolt holes, tighten it with a nut or self-tapping bolt, and use the axial preload of the bolt to "clamp" the two lifting rings, so that the mating surfaces fit tightly together to form an integral structure.

[0061] Optionally, the first airfoil lifting ring 21 has a countersunk through hole 25; the second airfoil lifting ring 22 has a threaded hole (not shown in the figure); wherein the axis of the countersunk through hole 25 coincides with that of the threaded hole. See reference. Figure 3 The concealed bolt installation method (countersunk design, non-flow-facing arrangement) avoids creating protrusions on the airfoil surface, preventing the introduction of "bolt resistance." Compared to welding, snap-fit, and other connection methods that may compromise surface smoothness, this method is better suited to the low-resistance requirements of wide-speed-range AUVs. Specifically, the countersunk portion can accommodate the bolt head, preventing it from protruding from the flow-facing surface (outer surface of the airfoil) of the first airfoil lifting ring 21, thus preventing the formation of "flow obstruction points" or eddies, and ensuring smooth water flow along the airfoil surface. The threaded hole is located on the inner side (coiling surface) of the second airfoil lifting ring 22, not directly contacting the external water flow. This avoids interfering with the flow field and ensures fastening strength through the threaded connection, preventing bolt loosening.

[0062] In this embodiment, the countersunk hole 25 of the first wing-shaped lifting ring 21 and the threaded hole of the second wing-shaped lifting ring 22 are precisely matched structures. Installation follows a three-step logic: "positioning, bolting, and tightening": Positioning and Alignment: The two wing-shaped lifting rings are aligned in the designed direction, ensuring the countersunk hole 25 of the first wing-shaped lifting ring 21 and the threaded hole of the second wing-shaped lifting ring 22 are completely coaxially aligned, ensuring the bolt can be smoothly inserted and engage the threads. Bolt Assembly: The fastening bolt 24 is inserted from the countersunk hole 25 side of the first wing-shaped lifting ring 21. After the bolt shank passes through the hole, it engages with the threaded hole of the second wing-shaped lifting ring 22. Locking and Fixing: The bolt is tightened, utilizing the self-locking characteristic of the threads to generate axial preload, tightly clamping the two lifting rings together. Simultaneously, the bolt head is completely recessed into the countersunk hole 25, flush with the outer surface of the first wing-shaped lifting ring 21.

[0063] If the lifting rings need to be disassembled, simply unscrew the bolts from the first wing-shaped lifting ring 21 side to separate the two lifting rings without damaging the structure. If the bolts or threaded holes are damaged, the corresponding parts can be replaced individually (e.g., tapping to repair the threaded holes), without replacing the entire lifting ring. By adjusting the diameter of the countersunk hole 25 and the specifications of the threaded hole, bolts of different strength grades (such as stainless steel bolts and high-strength alloy bolts) can be adapted to meet the strength requirements of the AUV under different operating environments (such as deep-sea high pressure and corrosive seawater). Optionally, after the bolts are tightened, a sealing washer (such as a rubber washer, not shown in the figure) can be installed between the countersunk hole 25 and the bolt head. Combined with the tightness of the threaded connection, this can effectively prevent seawater from seeping into the lifting ring or the AUV housing 1 from the orifice, reducing the risk of corrosion of internal components (such as bolts and lifting holes 23) and extending service life.

[0064] It is worth mentioning that, in this embodiment, after the first airfoil lifting ring 21 and the second airfoil lifting ring 22 are engaged and fixed to the original lifting ring 11 of the AUV housing 1 by friction. At this time, a relief groove (not shown in the figure) is provided on the mating surface of the first airfoil lifting ring 21 and the second airfoil lifting ring 22 to accommodate the original lifting ring 11. In an optional embodiment, a snap-fit ​​ring (not shown in the figure) can be extended axially along the lifting hole 23 at the relief groove of the first airfoil lifting ring 21 and / or the second airfoil lifting ring 22. The snap-fit ​​ring can be inserted into the lifting hole 23 of the original lifting ring 11, thereby enhancing the snap-fit ​​connection between the drag-reducing airfoil lifting ring and the original lifting ring 11, making the connection between the two more stable. Designers can adjust the connection relationship between the two according to the working conditions. This embodiment does not impose strict limitations on this, as long as the two do not fall off under the corresponding working conditions.

[0065] Continue reading Figure 2 and Figure 3The first airfoil lifting ring 21 or the second airfoil lifting ring 22 includes a leading edge side 26, a mid-section side 27, a rear section side 28, and a tail end side 29. Specifically, along the first direction, from the leading edge side 26 to the mid-section side 27, the projected thickness of the first airfoil lifting ring 21 or the second airfoil lifting ring 22 along the second direction gradually increases; along the first direction, from the rear section side 28 to the tail end side 29, the projected thickness of the first airfoil lifting ring 21 or the second airfoil lifting ring 22 along the second direction gradually decreases; the length of the mid-section side 27 is less than the length of the rear section side 28.

[0066] The thickness design of the drag-reducing airfoil shroud is strictly matched to the flow pattern of water on the airfoil surface. A "gradual thickness" guides the water flow in an orderly manner, avoiding turbulence. The thickness variation is designed along the flight direction to ensure the shroud always faces the oncoming flow at the "optimal angle of attack." Whether the AUV is cruising at low speeds or maneuvering at high speeds, the water flow can follow a pre-defined, gradually varying thickness path, adapting to a wide speed range of 3-50 knots. Specifically, in the first direction, which is the AUV's forward direction, the water first contacts the leading edge 26 of the shroud. The leading edge 26 is relatively thin and has a rounded outline, allowing the water flow to "smoothly separate" (rather than impact-like). As it transitions towards the mid-section 27, the thickness gradually increases, allowing the water flow to smoothly adhere to the thickened airfoil surface, avoiding "flow separation" (where the water prematurely detaches from the surface and forms eddies) near the leading edge. The mid-section 27 is the "maximum thickness point" of the shroud, where the water velocity reaches a stable state and the pressure distribution is uniform, laying the foundation for subsequent flow. After passing through the middle section 27, the water flows into the thickness-decreasing region from the rear section 28 to the tail section 29. The gradually thinning profile guides the water flow to "merge in an orderly manner," rather than causing the water flow to squeeze and become turbulent due to sudden contraction. The tail section 29 is the thinnest and has a sharp shape, which allows the diverted water flow to merge smoothly here, minimizing eddies in the wake region (eddies are the main source of pressure drag and flow-induced noise).

[0067] For example, the ends of the leading edge 26 and the tail end 29 that are opposite to each other are smooth chamfers 3, and the angle of attack of the tail end 29 is smaller than the angle of attack of the leading edge 26. The smooth chamfers 3, rather than sharp right angles, at the ends of the leading edge 26 and the tail end 29 that are opposite to each other (i.e., the foremost and rearmost edges of the lifting ring) are used to avoid "impact-type diversion" or "stuck-type convergence" of the water flow. For example, when the leading edge 26 is smoothly chamfered 3, the water flow first contacts the leading edge. The smooth chamfer 3 can change the incoming flow from "vertical impact" to "gentle diversion", reducing the impact turbulence of the water flow at the edge, avoiding the formation of local high-pressure areas, and reducing impact resistance. After the water flow passes through the lifting ring, it converges at the tail end. The smooth chamfer 3 of the tail end 29 can guide the water flow from "sudden compression and convergence" to "orderly convergence", avoiding the formation of vortices at the tail end edge (right-angled edges easily cause the water flow to detach at this point, generating wake vortices), and weakening wake resistance.

[0068] Understandably, the "angle of attack" refers to the angle between the end chamfered surface and the AUV's forward direction (first direction). The tail-end angle of attack is smaller than the leading-edge angle of attack, which is based on the design of "different flow states of water at the leading and tail ends." The leading-edge side 26 needs to cope with "incoming flow impact." A larger angle of attack (such as 30°-45°) allows the chamfered surface to better conform to the incoming flow direction, increasing the water flow contact area, dispersing the impact load, and avoiding excessively high local flow velocities that could lead to flow separation. The tail-end side 29 needs to achieve "rapid water flow convergence." A smaller angle of attack (such as 15°-30°) allows the chamfered surface to be steeper, guiding the water flow to converge quickly, shortening the wake length (the longer the wake, the greater the pressure drag), and simultaneously reducing the residence time of the water flow at the tail end, thus reducing the probability of eddy formation.

[0069] Furthermore, in this embodiment, the leading edge side 26 and the tail end side 29 are provided with rounded chamfers 4 on their sides away from the AUV housing 1. These edges, away from the AUV, are the direct contact edges between the lifting ring and the water flow. The rounded chamfers 4 guide the water flow by changing the edge shape. The water flow first contacts the outer edge of the leading edge, and the rounded contour of the rounded chamfer 4 on the leading edge side 26 allows the incoming flow to change from "impact-type diversion" to "smooth transition diversion along the rounded surface." Compared to sharp edges, the rounded surface can disperse the impact force of the water flow, avoiding the formation of local high-speed turbulence at the edge (high-speed turbulence directly increases frictional resistance and noise), while allowing the water flow to adhere more stably to the lifting ring surface, laying the foundation for subsequent gradual flow along the airfoil thickness.

[0070] After flowing through the lifting ring, the water converges at the outer edge of the tail end. The rounded chamfer 4 on the tail end side guides the water flow from a "sudden convergence" to a "gentle convergence along the arc surface," avoiding "water flow detachment" caused by sharp edges (water flow detachment will form a wake vortex), shortening the wake region length, and reducing the contribution of wake vortex to pressure drag. The "side away from the AUV" is the flow-facing surface (outer surface) of the lifting ring, while the side facing the AUV needs to be installed flush with the housing 1, without additional chamfering. The "chamfering only on the outer edge" design in this embodiment ensures optimized flow field in the key area in contact with the water flow, without affecting the fit between the lifting ring and the AUV housing 1, avoiding installation gaps caused by chamfering, and balancing drag reduction and structural compatibility.

[0071] In one embodiment, the connection between the leading edge side 26 and the tail side 29 is smooth, and the lifting hole 23 is located at the connection between the middle section side 27 and the rear section side 28. The thickness variation in different regions (thickening from the leading edge to the middle section and thinning from the rear section to the tail) is transitioned through a smooth curve to avoid flow field turbulence caused by abrupt thickness changes, ensuring that the flow field remains stable in all velocity ranges (3-50kn). Meanwhile, according to the flow field characteristics of NACA symmetrical airfoils, the middle section side 27 is the region of maximum thickness, where the water flow velocity is stable and the pressure distribution is uniform, making it the region with the most stable flow field; the rear section side 28 is the region of decreasing thickness, where the water flows orderly towards the tail along a gradually changing surface. The flow field at the connection point has neither the impact turbulence of the leading edge nor the converging vortices of the tail, belonging to a "low-disturbance flow field region". If the lifting hole 23 is located in a flow-sensitive area (such as the leading edge side 26, which can easily aggravate impact drag; or the tail end side 29, which can easily expand the wake vortex), it will disrupt the continuity of the water flow and introduce additional drag and noise. However, if the lifting hole 23 is located at the junction of the middle and rear sections, it will have minimal disturbance to the stable flow field and can maintain the low drag characteristics of the airfoil.

[0072] In one embodiment, the leading edge side 26, the middle section side 27, the rear section side 28, and the tail end side 29 are integrally molded. It should be noted that integral molding refers to creating an unseparable, single structure from the four sides using processes such as casting, 3D printing, or integral machining, rather than splicing multiple parts. Integral molding eliminates any seam marks and ensures uniform structural strength distribution. Underwater high pressure and corrosive environments accelerate corrosion of seams (seawater seeps into the seams, causing internal rust); the seamless, integral design completely avoids this problem, extending the lifespan of the lifting ring.

[0073] In one embodiment, the drag-reducing airfoil lifting ring is made of titanium alloy, duplex stainless steel, or carbon fiber reinforced polymer (CFRP). In this embodiment, titanium alloy (such as TC4 or TA2) is currently the preferred material for wide-speed-range AUV lifting rings, especially suitable for deep-sea and long-cycle operations, with its core advantages perfectly matching the requirements. Duplex stainless steel (such as 2205 or 2507) is a cost-effective alternative to titanium alloy. If the AUV has special requirements for "extreme lightweight" or "non-magnetic" properties (such as military stealth or magnetic detection missions), carbon fiber reinforced polymer will be selected. Titanium alloy is difficult to process and expensive, suitable for high-end needs; duplex stainless steel has mature technology and controllable costs, suitable for mass production; CFRP requires custom reinforcement, suitable for special scenarios. Designers can choose the appropriate material according to design requirements; this application does not impose strict limitations.

[0074] Based on the above structure, CFD simulation was carried out on the aircraft to calculate the hydrodynamic coefficients and the distribution of the surrounding flow field (pressure / velocity field) under three working conditions: no lifting ring, original lifting ring, and airfoil lifting ring, so as to quantitatively evaluate the drag reduction optimization effect of airfoil lifting ring.

[0075] Table 1 Comparison of aircraft drag values ​​under different operating conditions

[0076]

[0077] As shown in Table 1, it can be seen that the airfoil-shaped lifting rings significantly reduce the additional drag caused by the lifting rings on the aircraft.

[0078] Figure 4 The pressure coefficients on the upper surface of the hull are shown under different speed conditions. For example... Figure 4 As shown in the pressure distribution curves, compared to a vehicle without a lifting ring, the presence of the lifting ring causes significant local pressure fluctuations at its installation location: a high-pressure zone forms at the leading edge of the lifting ring, while a low-pressure zone appears at the trailing edge. This resulting reverse pressure gradient leads to increased drag. Except for the area near the lifting ring, the pressure distribution on the vehicle surface is basically the same under the three operating conditions: no lifting ring, existing lifting ring, and airfoil lifting ring.

[0079] Figure 5 The pressure coefficient of the upper surface of the hull is shown under the condition of v=15kn; Figure 6 The pressure coefficient of the upper surface of the hull is shown under the condition of v=50kn. Figure 5 and Figure 6 The pressure coefficient diagrams show that, under different positions and velocity conditions, the airfoil-shaped lifting ring significantly reduces the intensity and extent of the high-pressure region at the leading edge and the low-pressure region at the trailing edge compared to the original lifting ring. This improvement in flow field characteristics effectively reduces the additional pressure drag dominated by the reverse pressure gradient.

[0080] To visually demonstrate the impact of the ring shape on the pressure distribution around the aircraft, Figure 7 and Figure 8 The pressure cloud diagrams of the original lifting ring and the airfoil lifting ring at the forward position of the hull are shown under a speed of 15 knots. A comparison reveals that the high-pressure zone at the leading edge of the original lifting ring is significantly larger in both area and intensity than that of the airfoil lifting ring.

[0081] Figure 9 The vorticity diagram is shown when the original lifting ring is positioned at the front of the hull. Figure 10 The diagram shows the vorticity when the airfoil ring is positioned at the forward side of the hull. (See diagram for example.) Figure 9 and 10 As shown, in addition to effectively reducing the aircraft's drag, the vortex distribution at a speed of 15kn... Figure 9 and Figure 10It is clearly shown that the airfoil-shaped airfoil also has the effect of significantly optimizing the tail flow field structure. Its streamlined design can effectively suppress the generation and development of flow separation behind the airfoil, significantly reduce the size of the separation zone, and simultaneously weaken the vortex intensity in this area, thereby helping to reduce flow-induced noise and improve the adverse effects on the aircraft's maneuverability and stability caused by the presence of the airfoil.

[0082] Figure 11 The vorticity diagram of the original lifting ring at y=0.31 is shown; Figure 12 The vorticity diagram of the airfoil lifting ring at y=0.31 is shown. Figure 11 and Figure 12 As shown, in order to better analyze the influence of different ring shapes on vorticity distribution, quantitative analysis of the vorticity field at the y=0.31 section was conducted. The comparison revealed that, compared with the original ring, the airfoil ring can significantly reduce the vorticity intensity in the ring wake region, and the transition of the flow structure is smoother.

[0083] In summary, this application designs the airfoil structure as a symmetrical split type, which can be easily integrated into the existing lifting ring base using countersunk fastening screws. This design retains the original lifting ring mounting interface while achieving rapid assembly and disassembly, ensuring a simple and reliable structure. The airfoil profile uses the mature and reliable NACA series symmetrical airfoil. This airfoil is supported by a rich public hydrodynamic database and has been verified through extensive engineering practice. Its low-drag characteristics effectively improve the flow structure around the AUV hull and lifting ring, significantly suppressing flow separation, thereby reducing navigation drag and propulsion energy consumption, and effectively reducing flow-induced noise.

[0084] The positional relationships, quantity, and structural shape of the various components of the drag-reducing airfoil lifting ring provided in this application are not limited to the above embodiments. All technical solutions implemented under the principles of this application are within the protection scope of this solution. Any one or more embodiments or illustrations in the specification, combined in a suitable manner, are within the protection scope of this solution.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application. Those skilled in the art should understand that although this application has been described in detail with reference to the foregoing embodiments, modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. These modifications or substitutions do not cause the essence of the corresponding technical solutions to depart from the spirit and scope of the technical solutions in the embodiments of this application.

Claims

1. A drag-reducing airfoil lifting ring, characterized in that, include: The lifting ring body has an airfoil of NACA symmetric shape and includes two axisymmetric first airfoil lifting rings and second airfoil lifting rings. The first and second airfoil lifting rings have two convex arcuate surfaces on their opposite sides, with lifting holes for launching and suspending autonomous underwater vehicles (AUVs) at the protrusions. The first or second airfoil lifting ring includes a leading edge side, a mid-section side, a rear section side, and a tail end side. Along a first direction, from the leading edge side to the mid-section side, the projected thickness of the first or second airfoil lifting ring along a second direction gradually increases; along the first direction, from the rear section side to the tail end side, the projected thickness of the first or second airfoil lifting ring along the second direction gradually decreases. The length of the mid-section side is less than the length of the rear section side. The first direction is the forward direction of the AUV, and the second direction is perpendicular to the first direction.

2. The drag-reducing airfoil lifting ring according to claim 1, characterized in that, After the first and second airfoil-shaped lifting rings are engaged with each other, they can be detachably installed on the autonomous underwater vehicle (AUV).

3. The drag-reducing airfoil lifting ring according to claim 1, characterized in that, The first airfoil and the second airfoil are connected to each other by fastening bolts.

4. The drag-reducing airfoil lifting ring according to claim 3, characterized in that, The first airfoil lifting ring has a countersunk through hole; the second airfoil lifting ring has a threaded hole.

5. The drag-reducing airfoil lifting ring according to claim 1, characterized in that, The ends of the leading edge and the tail end that are opposite to each other are smooth chamfered, and the angle of attack of the tail end is smaller than the angle of attack of the leading edge.

6. The drag-reducing airfoil lifting ring according to claim 1, characterized in that, The leading edge and tail end sides facing away from the AUV have rounded chamfers.

7. The drag-reducing airfoil lifting ring according to claim 1, characterized in that, The lifting hole is located at the connection between the middle section and the rear section.

8. The drag-reducing airfoil lifting ring according to claim 7, characterized in that, The connection between the leading edge side and the tail end side is a smooth connection, and the leading edge side, the middle section side, the rear section side and the tail end side are integrally formed.

9. A wide-speed-range AUV, characterized in that, Includes the drag-reducing airfoil lifting ring as described in any one of claims 1-8.

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