Hole-slot combined bubble drag reduction device

Abstract

The present invention relates to a combined hole and slit bubble drag reduction device, which comprises a plurality of cavities arranged on the ship bottom plate. A bubble generator is arranged in each cavity. The bubble generator includes a first bubble generator and a plurality of second bubble generators. The upper part of the cavity is connected to a gas source through a pipeline. The first bubble generator is a slit-shaped foaming device, and the second bubble generator is a hole-shaped bubble generator. The first bubble generator and the second bubble generators are arranged symmetrically in the transverse direction and longitudinally distributed on the ship bottom plate. The first bubble generator is arranged near the bow of the ship, and the second bubble generators are arranged in the middle and at the tail of the ship. The first bubble generator is a bubble generator with a rectangular slit-shaped opening, and a square flow guiding wall is arranged at the rectangular packaging opening of the first bubble generator. The present invention increases the area of bubble generation and fusion at the ship bottom, forms a relatively stable and uniform gas layer on the ship bottom surface, and improves the drag reduction efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of drag reduction for ships and ocean engineering, and more specifically, to a combined hole and slit bubble drag reduction device. Background Art

[0002] Frictional resistance is an important part of the resistance suffered by the hull. The mechanism of gas drag reduction technology is clear, and it is one of the most promising technologies to significantly reduce the frictional resistance of ships. The gas drag reduction technology releases gas underwater to form a uniform gas film between part of the wet surface of the ship and water, reducing the hydrodynamic viscosity of part of the wet surface of the ship and achieving the purpose of significantly reducing frictional resistance.

[0003] There are usually two forms of releasing gas in existing gas drag reduction devices. One is to release bubbles through holes or generate bubbles using porous media (Wang Jiamei, Jiang Mansong, Zheng Xiaowei, etc. Experimental study on drag reduction of ship micro-bubbles under different jetting forms in a water tank [J]. Journal of Huazhong University of Science and Technology (Natural Science Edition), 2004, 32(12): 78-80. DOI: 10.3321 / j.issn: 1671-4512.2004.12.028.); the other is to release gas through slender spray slits on the hull surface. The bubbles emitted by the former are difficult to fuse and are not easy to form a uniform gas layer on the bottom plate of the ship, affecting the drag reduction effect. The bubble fusion of the latter is better than that of the former, and it is easier to achieve the maximum drag reduction effect under the same gas injection volume as the former, but the adhesion of the formed gas layer is poor (Hao, W U., Yongpeng, O., & Qing, Y.E. (2019). Experimental study of air layer drag reduction on a flat plate and bottom hull of a ship with cavity. Ocean Engineering, 183, 236–248.).

[0004] The use of steps and grooves on the bottom plate of the ship can better improve the gas layer situation on the bottom plate of the ship. However, whether it is the use of steps or grooves, it has a certain impact on the hull form. This not only increases the processing difficulty and cost of the ship, but also may increase the form resistance of the ship. In addition, the existence of grooves is also a great test for the strength of the bottom plate of the ship. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a combined hole and slit bubble drag reduction device, which combines hole-shaped jetting and slit-shaped jetting to promote the fusion of bubbles on the bottom plate of the ship, and at the same time does not change the hull form of the bottom plate of the ship. On this basis, the area where bubbles on the bottom plate of the ship fuse is increased, so as to form a relatively stable and uniform gas layer on the surface of the bottom plate of the ship and improve the drag reduction efficiency.

[0006] The technical solution adopted by the present invention to solve its technical problems is: to construct a combined pore and slit bubble drag reduction device, including a plurality of cavities provided on the ship bottom plate, a bubble generator is arranged in the cavity, the bubble generator includes a first bubble generator and a plurality of second bubble generators, the cavity is connected to a gas source through a pipeline above, the first bubble generator is a slit-shaped foamer, the second bubble generator is a pore-shaped bubble generator, the first bubble generator and the second bubble generators are arranged symmetrically horizontally and longitudinally on the ship bottom plate, the first bubble generator is arranged near the ship bow, and the second bubble generators are arranged in the middle and at the tail of the ship;

[0007] The first bubble generator is a bubble generator with a rectangular slit-shaped opening, a square flow guiding wall is arranged at the rectangular packaging opening of the first bubble generator, the bottom of the square flow guiding wall is fixed to the ship bottom plate through a bearing structure, and the middle parts of the two outer sides of the square flow guiding wall are connected to a push-pull rod through a sliding shaft;

[0008] The second bubble generator is a bubble generator with a circular opening, a jet pipe is arranged above the circular opening of the second bubble generator, the bottom of the jet pipe is connected to the opening section of the ship bottom plate through an elastic sealing ring, and the middle of the jet pipe is fixed through a bearing structure.

[0009] According to the above solution, there are two second bubble generators, namely a front second bubble generator and a rear second bubble generator, the first bubble generator is arranged at 0.3B - 0.35B in the ship length direction at the front edge of the ship shoulder, the front second bubble generator is arranged at 0.25B - 0.3B behind the ship shoulder, and the rear second bubble generator is arranged at 1B - 1.05B in the ship length direction behind the position where the front second bubble generator is arranged, and B is the maximum width of the ship bottom.

[0010] According to the above solution, the width of the rectangular packaging opening of the first bubble generator is 3mm - 5mm, the diameter of the circular opening of the second bubble generator is 4mm - 6mm, and the circular openings opened by the second bubble generator are evenly distributed in a row.

[0011] According to the above solution, a flow control valve for controlling the gas volume or whether the bubble generator works is arranged on the pipeline.

[0012] According to the above solution, the bottom of the square flow guiding wall and the ship bottom plate are arranged on the same horizontal plane.

[0013] According to the above solution, the jet pipe is cylindrical, and the diameter of the jet pipe is 2mm - 4mm.

[0014] Implementing the combined pore and slit bubble drag reduction device of the present invention has the following beneficial effects:

[0015] 1. The bubble drag reduction device with combined orifices and slots provided by the present invention has the slots in front and the orifices behind. Utilizing the characteristics of high initial fusion degree and preliminary penetration of the bubble jets from the slots, it promotes the overall fusion of the bubbles on the ship bottom plate, while not changing the shape of the ship bottom plate.

[0016] 2. Through a large number of numerical simulations, the present invention determines the arrangement of the bubble generators with orifices and slots when the bubble fusion is in the best condition at different ship speeds, optimizes the fusion effect, thereby increasing the area where the bubbles on the ship bottom plate fuse, quickly forming a relatively stable and uniform gas layer on the surface of the ship bottom plate, and improving the drag reduction efficiency.

[0017] 3. The present invention absorbs the advantages of the existing single-orifice bubble drag reduction device with good bubble adhesion and the single-slot bubble drag reduction device with good bubble fusion and rapid gas layer formation, and makes up for their shortfalls to a certain extent, avoiding the negative effects of steps and grooves on the shape of the ship bottom plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention will be further described below in conjunction with the drawings and embodiments. In the drawings:

[0019] Figure 1 is a top view structural schematic diagram of the bubble drag reduction device with combined orifices and slots of the present invention;

[0020] Figure 2 is a side view structural schematic diagram of the bubble drag reduction device with combined orifices and slots of the present invention;

[0021] Figure 3 is a partial enlarged view of the bubble drag reduction device with combined orifices and slots of the present invention;

[0022] Figure 4 is a partial enlarged top view of the orifice structure of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] For a clearer understanding of the technical features, objectives, and effects of the present invention, the specific embodiments of the present invention will now be described in detail with reference to the drawings.

[0024] As Figures 1-4 shown, the bubble drag reduction device with combined orifices and slots of the present invention includes a plurality of cavities 5 provided on the ship bottom plate 4. A bubble generator is arranged in the cavity 5. The bubble generator includes a first bubble generator 1 and a plurality of second bubble generators 2. The upper part of the cavity 5 is connected to a gas source 6 through a pipeline. The first bubble generator 1 is a slot-shaped foaming device, and the second bubble generator 2 is an orifice-shaped bubble generator. The first bubble generator 1 and the second bubble generators 2 are arranged symmetrically horizontally and longitudinally on the ship bottom plate 4. The first bubble generator 1 is arranged near the bow, and the second bubble generators 2 are arranged in the middle and at the stern of the ship.

[0025] The first bubble generator 1 is a bubble generator with a rectangular slit-shaped opening. A square flow guide wall 9 is arranged at the rectangular encapsulation opening of the first bubble generator 1, and the bottom of the square flow guide wall 9 and the ship bottom plate 4 are arranged on the same horizontal plane. The bottom of the square flow guide wall 9 is fixed to the ship bottom plate 4 through a bearing structure 8, and the middle parts of the two outer sides of the square flow guide wall 9 are connected to the push-pull rod 7 through sliding shafts 12; the second bubble generator 2 is a bubble generator with a circular opening. An air injection pipe is arranged above the circular opening of the second bubble generator 2. The air injection pipe is cylindrical, and the diameter of the air injection pipe is 2 mm to 4 mm. The bottom of the air injection pipe is connected to the opening section of the ship bottom plate 4 through an elastic sealing ring 11, and the middle of the air injection pipe is fixed through a bearing structure 8. There are two second front bubble generators 3 and 13 respectively for the second bubble generator 2. The first bubble generator 1 is arranged at 0.3B to 0.35B in the ship length direction at the front edge of the ship's shoulder. The second front bubble generator 3 is arranged at 0.25B to 0.3B behind the ship's shoulder. The second rear bubble generator 13 is arranged at 1B to 1.05B behind the second front bubble generator 3 in the ship length direction, where B is the maximum width of the ship bottom. The width of the rectangular encapsulation opening of the first bubble generator 1 is 3 mm to 5 mm. The second bubble generator 2 has a circular opening with a diameter of 4 mm to 6 mm, and the circular openings opened by the second bubble generator 2 are evenly distributed in a row.

[0026] The hole-slit combined bubble drag reduction device of the present invention includes a group of slit-shaped bubble generators and multiple groups of hole-shaped bubble generators. The slit-shaped bubble generator is arranged close to the bow and is the first bubble generator 1; the hole-shaped bubble generators are a row of circular openings, which are sequentially located behind the slit-shaped generator. In this embodiment, according to the ship length and width, the number is set to include 2, namely the second front bubble generator 3 and the second rear bubble generator 13 respectively. The hole-slit combined bubble drag reduction device is longitudinally distributed on the ship bottom plate 4 and is symmetrically arranged transversely. A group of slit-shaped bubble generators are in the front, which is the first bubble generator 1, and two groups of hole-shaped bubble generators are in the rear, which are the second front bubble generator 3 and the second rear bubble generator 13 respectively. Each bubble generator is symmetrically distributed longitudinally on the ship bottom plate 4, and the angles of the gas outlets of the jet slits and the jet holes can be adjusted according to the ship speed. Based on the conclusions of numerical simulation studies, the jet holes and jet slits are reasonably distributed at specific positions on the ship bottom plate 4. By utilizing the movement and fusion characteristics of the bubbles ejected from the holes and slits, a reliable hole-slit combined scheme is formulated. Compared with the single hole or slit-shaped bubble drag reduction device, it can form a more uniform, more stable and larger coverage gas layer, and has a better drag reduction effect. The flat-bottom ship is a typical structure of a ship. The structure of the flat-bottom part of the ship bottom is suitable for the attachment of microbubbles. For some ships with a flat-bottom structure, such as wide and flat river-sea through ships, the frictional resistance accounts for a relatively high proportion of the total resistance, and the benefits brought by the bubble drag reduction device are also relatively large; the present invention takes it as an example for illustration, which has good demonstration significance, but does not mean that this device is only applicable to the ships shown or flat-bottom ships.

[0027] In a preferred embodiment of the present invention, the first bubble generator 1 is located at 0.3B to 0.35B (B is the maximum width of the hull bottom) in the longitudinal direction of the hull shoulder front edge, and is a rectangular slit-like opening with a width of 3 mm to 5 mm, and the opening length is determined by the hull bottom width B; the front second bubble generator 3 is located at 0.25B to 0.3B behind the hull shoulder, and is a row of circular openings with an opening diameter range of 4 mm to 6 mm, and the number of openings is determined by the hull bottom width B, and the distance between the circular openings is equal and evenly distributed; since the length of the bottom plate 4 of this example ship is relatively large, the rear second bubble generator 13 is provided, which is located at 2.45B to 2.5B in the longitudinal direction of the ship's bow rear edge, and is also a row of circular openings; the slit spray will form a relatively large bubble with preliminary internal fusion and penetration in the front, which is easy to fuse the relatively isolated string-like bubbles of the subsequent hole spray, and will fill the gaps between the string-like bubbles of the hole spray, promoting their circumferential fusion. The distances between different bubble generators, the number of openings, and the gas volume distribution are based on the conclusions of a large number of numerical simulation studies. Inappropriate distances and the number of openings will affect the bubble fusion effect and even reduce the bubble drag reduction effect. All bubble generators are arranged in the cavity 5, and the cavity 5 is connected to the gas source 6 through a pipeline above. The cavity of the cavity 5 can adjust the pressure before the gas is ejected, reduce the pressure pulsation, and use devices such as flow valves to control the gas volume or control whether the bubble generator works.

[0028] In a preferred embodiment of the present invention, a square guide wall 9 is provided in the spray slit of the first bubble generator 1. The bottom of the square guide wall 9 is on the same horizontal plane as the bottom plate 4 of the ship, always ensuring the flatness of the surface of the bottom plate 4 of the ship and avoiding an increase in form drag. The square guide wall 9 pushes the front and rear wall surfaces by the push-pull rod 7, and the push-pull rod 7 is fixed to the square guide wall 9 through the sliding shaft 12 to achieve the effect of hinging. The bottom of the square guide wall 9 is fixed to the bottom plate 4 of the ship through the bearing structure 8, giving the square guide wall 9 the freedom of rotation. When the included angle between the gas ejection velocity direction and the normal of the bottom plate 4 of the ship decreases, the left push-pull rod 7 pulls to the left, and the right push-pull rod 7 pushes to the left synchronously; when the angle increases, the left push-pull rod 7 pushes to the right, and the right push-pull rod 7 pulls to the right synchronously. In the front second bubble generator 3 and the rear second bubble generator 13, a cylindrical air injection pipe is provided in each opening, with a diameter generally of 2 mm to 4 mm. The air injection pipe and the opening section of the bottom plate 4 of the ship are connected by an elastic sealing ring 11, and the middle is fixed to the outside of the front and rear (perpendicular to the picture and outward is the front) of the air injection pipe through the bearing structure 8, and the angle is adjusted in cooperation with the push-pull rod 7. At a certain ship speed, when the jet orifice exhausts at a certain inclination angle, the impedance effect between the jet orifice and the oncoming flow is weak, the pressure at the jet hole and the jet slit is smaller than that of the straight hole exhaust, the pressure difference between the cavity 5 and the bottom plate 4 of the ship is large, and the horizontal component velocity along the longitudinal direction of the ship to the stern is large, and an air layer can be formed on the bottom plate 4 of the ship faster. While the pressure distribution on the bottom plate 4 of the ship is more uniform, the flow stability of the bottom plate 4 of the ship is improved, and the annihilation of bubbles is further reduced.

[0029] The process of generating bubbles in the present invention is as follows:

[0030] The first bubble generator 1 has a slit-shaped opening, with a relatively large gas injection volume. The generated bubbles are relatively uneven, but the bubbles generated by slit injection are dense. The bubbles first undergo longitudinal and transverse fusion to form a relatively large bubble with a preliminary internal connection, and then move backward along the bottom plate under the action of the water flow on the ship bottom plate 4. At this time, the front second bubble generator 3 is also generating bubbles, but the generated bubbles are orifice injection bubbles. The bubbles generated by the front second bubble generator 3 are not fully fused and are relatively dispersed, shaped like a string. When the relatively large bubble with a preliminary internal connection in the front moves to the front second bubble generator 3, it absorbs and fuses more isolated microbubbles, and at the same time fills the gaps between the string-shaped bubbles, promoting their circumferential fusion, thereby forming a larger and more uniform internally connected bubble. Immediately afterwards, the connected bubble continues to move downward to the front second bubble generator 13, where more stable and thorough fusion occurs, thereby forming a continuous sheet of combined connected bubbles or an air layer on the entire ship bottom plate 4, reducing the viscosity and density of the boundary layer of the ship bottom plate 4, and achieving the purpose of significantly reducing the frictional resistance.

[0031] When the ship body is wider and longer, more branch pipes, corresponding valves, and corresponding cavities 5 can be provided. The cavity 5 can adjust the pressure before gas injection, reducing pressure pulsation. The cavity 5 of each bubble generator is divided into three parts, named the jetting areas 1.1, 1.2, 1.3, 3.1, 3.2, 3.3, 13.1, 13.2, and 13.3 from the bow to the stern and from the port side to the starboard side. The cooperation between different areas and gas volumes of the orifice-slit combined bubble generator will generate air layers with different coverage degrees on the ship bottom plate 4 at different Froude numbers of the ship. More precise control will enable the ship to obtain a better drag reduction effect. The position of the bubble generator can be appropriately adjusted to meet the drag reduction requirements of ships with different hull forms. The second bubble generator 2 - the multi-orifice bubble generator can be replaced with a single-orifice jetting device with a larger area, in order to form different combined jetting forms and achieve a better drag reduction effect.

[0032] The embodiments of the present invention have been described above in conjunction with the accompanying drawings. However, the present invention is not limited to the above specific embodiments. The above specific embodiments are merely illustrative and not restrictive. Under the inspiration of the present invention, those of ordinary skill in the art can also make many forms without departing from the spirit and scope protected by the claims of the present invention, and all of these fall within the protection scope of the present invention.

Claims

1. A combined hole and slit air bubble drag reduction device, comprising a plurality of cavities arranged on the ship bottom plate, characterized in that, A bubble generator is arranged in the cavity. The bubble generator includes a first bubble generator and multiple second bubble generators. The upper part of the cavity is connected to a gas source through a pipeline. The first bubble generator is a slit-shaped foamer, and the second bubble generator is a hole-shaped bubble generator. The first bubble generator and the second bubble generators are arranged symmetrically horizontally and longitudinally on the ship bottom plate. The first bubble generator is arranged near the bow of the ship, and the second bubble generators are arranged in the middle and at the stern of the ship; The first bubble generator is a bubble generator with a rectangular slit-shaped opening. A square diversion wall is arranged at the rectangular encapsulation opening of the first bubble generator. The bottom of the square diversion wall is fixed to the ship bottom plate through a bearing structure. The middle parts of the two outer sides of the square diversion wall are connected to a push-pull rod through sliding shafts; The second bubble generator is a bubble generator with a circular opening. An air injection pipe is arranged above the circular opening of the second bubble generator. The bottom of the air injection pipe is connected to the opening section of the ship bottom plate through an elastic sealing ring. The middle part of the air injection pipe is fixed through a bearing structure.

2. The combined orifice and slit bubble drag reduction device according to claim 1, characterized in that, There are two second bubble generators, namely a front second bubble generator and a rear second bubble generator. The first bubble generator is arranged at 0.3B - 0.35B in the ship length direction at the front edge of the ship's shoulder. The front second bubble generator is arranged at 0.25B - 0.3B behind the ship's shoulder. The rear second bubble generator is arranged at 1B - 1.05B behind the front second bubble generator in the ship length direction, where B is the maximum width of the ship bottom.

3. The pore and slit combined bubble drag reduction device according to claim 2, wherein, The width of the rectangular encapsulation opening of the first bubble generator is 3mm - 5mm. The second bubble generator has a circular opening with a diameter of 4mm - 6mm. The circular openings opened by the second bubble generator are evenly distributed in a row.

4. The pore and slit combined bubble drag reduction device according to claim 1, wherein A flow control valve for controlling the gas volume or whether the bubble generator works is arranged on the pipeline.

5. The pore and slit combined bubble drag reduction device according to claim 1, characterized in that, The bottom of the square diversion wall and the ship bottom plate are arranged on the same horizontal plane.

6. The pore and slit combined bubble drag reduction device according to claim 1, characterized in that, The air injection pipe is cylindrical, and the diameter of the air injection pipe is 2mm - 4mm.

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