A two-dimensional water tunnel experimental device and its control method and application

Abstract

The present invention discloses a two-dimensional water tunnel experimental device, a control method and an application thereof, comprising soap liquid, an upper water tank and a lower water tank, wherein a nozzle is connected to the bottom of the upper water tank, and two nylon ropes are connected to the nozzle outlet, and the soap liquid forms a soap film layer between the nylon ropes on both sides that gradually expands downward, and glass plates are respectively provided on the front and back sides of the soap film layer, and hooks are respectively provided on the upper and lower sides of the nylon ropes, and weights are hung on the lower ends of the nylon ropes, and the weights are immersed in the lower water tank, and a reflux channel is provided between the upper and lower water tanks. The present invention avoids the influence of surface tension on the soap film layer by hanging weights on the lower ends of the nylon ropes on both sides, and at the same time, glass clamps are provided on the front and back sides of the soap film layer to constrain the air flow field on both sides of the soap film layer, thereby forming a spatially steady-state turbulent field, thereby preventing the soap film layer from flowing downstream and the turbulent field from gradually weakening.

Description

Technical Field

[0001] The present invention relates to the field of fluid experiments, in particular to a two-dimensional water tunnel experimental device and a control method thereof. Background Art

[0002] Water tunnels and wind tunnels are commonly used fluid mechanics experimental test devices. Three-dimensional wind tunnels and water tunnels are widely used in the design and performance testing of automobiles, aircraft, and submarines. In geophysics, the thickness of the ocean and atmosphere (about 10 km) is often one percent of the diameter of the earth and is often regarded as two-dimensional turbulence. Therefore, a two-dimensional water tunnel experimental device is needed to study earth science. Soap film has an extremely small thickness ratio (10 -4 ), which is often regarded as a two-dimensional fluid, and the two-dimensional water hole based on the soap film layer has unique scientific research and experimental value.

[0003] In the prior art, when using a soap film layer water tunnel device to conduct two-dimensional turbulence research, it is often necessary to achieve a spatially uniform steady-state turbulent field. The conventional way to achieve turbulence in the soap film layer process is to insert a comb-like grid upstream of the soap film layer. However, due to the disturbance of the grid, the turbulent field continues to decay in space, and a spatially steady-state turbulent field cannot be achieved. Chinese patent No. CN202011270786.0 discloses a "Soap Film Layer Water Tunnel Test Device". In the above scheme, due to the effect of surface tension, the soap film layer on the inside of the silk thread will stretch inward at the midstream position, forming a Laval tube-like flow channel section, resulting in the soap film layer boundary line not being vertical. There will be a process of first accelerating and then decelerating in the experimental section, which will lead to uneven flow velocity of the soap film layer, and it is impossible to meet the flow field performance requirements of the experimental process. Summary of the Invention

[0004] In order to solve the problems existing in the above-mentioned prior art, the present invention provides a two-dimensional water tunnel experimental device and a control method thereof. By hanging weights at the lower ends of nylon ropes on both sides, the influence of surface tension on the soap film layer is avoided. At the same time, glass plywood is arranged on the front and back sides of the soap film layer to constrain the air flow field on both sides of the soap film layer, forming a spatially steady-state turbulent field, preventing the turbulent field from gradually weakening as the soap film layer flows downstream.

[0005] The technical solutions of the present invention are as follows:

[0006] A two-dimensional water tunnel experimental device includes a first bracket, an upper water tank and a lower water tank. The bottom of the upper water tank is connected to a nozzle. Two nylon ropes are connected to the nozzle outlet. A soap film layer is formed between the nylon ropes on both sides. Glass plates are respectively provided on the front and back sides of the soap film layer. Hooks are respectively provided on the upper and lower sides of the two nylon ropes and between adjacent first brackets. Weights are hung at the lower ends of the nylon ropes. The weights are immersed in the lower water tank. A reflux channel is provided between the upper and lower water tanks.

[0007] Furthermore, the two-dimensional water tunnel experimental device also includes a second bracket arranged parallel to the first bracket.

[0008] Furthermore, the second bracket is fixed with a grid and a high-speed camera, the grid vertically passes through the upstream position of the soap film layer, and two high-speed cameras arranged in sequence along the flow direction are arranged in parallel outside the downstream position of the soap film layer.

[0009] Furthermore, at least one hinge is provided on the first bracket, and any one side of the front and rear glass plates are hinged by the hinge. After the glass plates on both sides are closed, the glass plates are respectively located on both sides of the soap film layer and are parallel to the soap film layer.

[0010] Furthermore, when the soap film layer flows, due to the effect of surface tension, the displacement of each nylon rope toward the inside of the soap film layer is Where γ is the surface tension of the soap film, m is the weight of a single weight, and X2 is the length of the experimental section.

[0011] Furthermore, the minimum weight of the weight is where δ y The maximum allowable shrinkage distance of the nylon rope.

[0012] Furthermore, a peristaltic pump is provided in the reflux channel.

[0013] Furthermore, the soap film layer comprises 2% by mass of dishwashing liquid, 10% by mass of glycerol, and 88% by mass of deionized water, and tracer particles are added to the soap film layer.

[0014] A control method for the above-mentioned two-dimensional water tunnel experimental device specifically includes the following steps:

[0015] (1) The soap liquid in the upper water tank flows out through the nozzle, forming the soap film layer between the nylon ropes on both sides;

[0016] (2) rotating the front and rear glass plates around the fixed ends respectively, and opening the movable ends of the front and rear glass plates to form a soap film layer adjustment space;

[0017] (3) The tracer particles in the soap film layer are illuminated by a pulsed laser, and the two high-speed cameras take pictures of the tracer particles facing each other. When the tracer particles fall on the camera focus plane with a depth of field of only 23 μm, the tracer particles are clearly imaged. Otherwise, the tracer particles are out of focus. Combined with the image, the four hooks are continuously adjusted until all the tracer particles are clearly imaged, indicating that the plane formed by the four hooks coincides with the camera focus plane, that is, the soap film layer is in the same plane;

[0018] (4) rotating the front and rear glass plates around the fixed ends respectively, and moving the front and rear glass plates closer to each other until the glass plates on both sides are parallel to the soap film layer;

[0019] (5) The soap film layer flows into the lower water tank and is sent into the upper water tank by the peristaltic pump.

[0020] The above-mentioned two-dimensional water tunnel experimental device is applied to various fluid mechanics experiments.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The parallel glass clamp device realizes a spatially stable turbulent field; the present invention is provided with glass clamps. The conventional way to realize turbulence in soap film flow is to insert a comb-like grid upstream of the soap film layer. However, the turbulent field formed by the grid disturbance is constantly attenuated in space and cannot form a stable turbulent field. Adding glass clamps on both sides of the soap film layer can limit the air boundary layer in space, thereby forming a spatially stable Poiseuille turbulent field.

[0023] (2) A specific soap solution formula achieves long-term stable flow; the soap solution used in the present invention uses a mass fraction of 2% dishwashing liquid, 10% glycerol and 88% deionized water to extend the running time of the soap film layer.

[0024] (3) The camera focus test method is used to ensure that the soap film is adjusted to one plane. The present invention sets two high-speed cameras, and the cameras focus on and shoot the corresponding soap film layers. Tracer particles are added to the soap solution. When the soap film layers are not in one plane, the tracer particles will be out of focus in the camera image. Combined with the camera image, the plane where the hook is located is continuously adjusted until all tracer particles are in focus. The soap film is in the same plane, that is, the focus plane of the camera.

[0025] (4) A weight of a specific weight is hung under the nylon rope of the present invention to verticalize the boundary of the soap film layer, thereby avoiding the nylon rope being stretched toward the soap liquid due to the effect of surface tension, resulting in a process of first accelerating and then decelerating, thereby ensuring the uniformity of the flow field. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the structure of the present invention;

[0027] Figure 2 Schematic diagram of the glass plate structure of the present invention;

[0028] Figure 3 Schematic diagram of the effect of surface tension on soap film layer.

[0029] In the accompanying drawings, the components represented by the reference numerals are as follows:

[0030] 1. First bracket; 2. Upper water tank; 3. Lower water tank; 4. Nozzle; 5. Nylon rope; 6. Soap film layer; 7. Glass plate; 8. Hook; 9. Weight; 10. Reflux channel; 11. Tracer particles; 12. Grid; 13. High-speed camera; 14. Hinge; 15. Peristaltic pump; 16. Second bracket. DETAILED DESCRIPTION

[0031] In order to make the contents of the present invention easier to understand, the technical solutions of the present invention are further described below in conjunction with specific implementation methods and drawings, but the present invention is not limited thereto.

[0032] See also Figure 1 、 Figure 2 and Figure 3 The invention provides a technical solution: a two-dimensional water tunnel experimental device, comprising a first bracket 1, an upper water tank 2 and a lower water tank 3. The upper water tank 2 is connected to a nozzle 4 at the bottom, and two nylon ropes 5 are connected to the outlet of the nozzle 4. The two nylon ropes 5 form expansion sections that are away from each other and test sections that are parallel to each other. A soap film layer 6 is formed between the nylon ropes 5 on both sides. The soap film layer 6 gradually expands under the action of the nylon ropes on both sides, and then continuously accelerates with gravity. Finally, it is fully developed in the test section to form a turbulent field. Glass plates 7 are respectively provided on the front and back sides of the soap film layer 6. Hooks 8 are respectively provided on the upper and lower sides of the two nylon ropes 5 and between the adjacent first brackets 1. A weight 9 is hung at the lower end of the nylon rope 5 to reduce the change in the central width of the test section of the soap film layer 6 and affect the verticality of the flow channel. The weight 9 is immersed in the lower water tank 3, and a reflux channel 10 is provided between the upper water tank 2 and the lower water tank 3.

[0033] Specifically, the soap film layer 6 comprises 2% dishwashing liquid, 10% glycerin, and 88% deionized water by weight. The dishwashing liquid provides a surfactant, the glycerin effectively increases the viscosity of the soap film layer 6, and the deionized water prevents impurities in the water from affecting the effectiveness of the surfactant. The concentration ratio of the three significantly affects the operating life of the soap film layer 6. This formulation allows the soap film layer 6 to operate stably for more than four hours. The soap film layer 6 also contains tracer particles 11. The tracer particles 11 have a diameter of 1 μm, which is smaller than the thickness of the soap film layer 6, thus negligible impact on the soap film layer 6.

[0034] Specifically, the two-dimensional water tunnel experimental device further includes a second bracket 16 arranged parallel to the first bracket 1 .

[0035] Specifically, the second bracket 16 is fixed with a horizontally arranged grid 12 and a high-speed camera 13. The grid 12 is made of an aluminum plate as a base, with semicircular grooves cut on the surface by wire cutting, stainless steel needles inserted as cylindrical rods, and fixed with magnets. The grid 12 passes vertically through the upstream position of the soap film layer 6. Two high-speed cameras 13 are arranged in parallel along the flow direction and outside the downstream position of the soap film layer 6. The two high-speed cameras 13 can adjust the soap film layer 6 to be in a plane; the depth of field of the macro lens is δ z =4(1+M) 2 If the macro lens reproduction ratio M = 1, the aperture number f = 2.8, and the light source wavelength λ = 532 nm, the depth of field is 23 μm. High-speed camera 13 is used to verify the focus of the soap film layer 6, ensuring that it is aligned on a single plane. Combined with the camera image, the position of hooks 8 in the yz plane is continuously adjusted. If the position of the tracer particles 11 is outside the depth of field (23 μm), the tracer particles 11 are out of focus. When all tracer particles 11 are in focus, the deviation in the z direction of the soap film layer 6 is guaranteed to be within 23 μm, which is much smaller than the width of the soap film layer 6 and even smaller than the meter-scale longitudinal dimension. This allows us to determine whether the four hooks 8 are aligned on the same plane, thus ensuring that the soap film layer 6 remains aligned.

[0036] Specifically, at least one hinge 14 is provided on the first bracket 1, and any side of the front and rear glass plates 7 is hinged by the hinge 14. In the experimental preparation stage, the front and rear glass plates 7 are respectively rotated around the hinge 14 so that the moving ends of the front and rear glass plates 7 are away from each other, so as to facilitate the debugging of the soap film layer 6; in the debugging end stage, the front and rear glass plates 7 are respectively rotated around the hinge 14 so that the moving ends of the front and rear glass plates 7 are close to each other until the glass plates 7 and the soap film layer 6 are parallel to each other, so as to constrain the air flow field on both sides of the soap film layer 6 and prevent the soap film layer 6 from flowing downstream and the turbulent field gradually weakening; at the same time, since the soap film layer 6 will form a strong turbulent pulsation after flowing through the grid 12, the turbulent field caused by it is continuously attenuated in space. The glass plates 7 on both sides can limit the air boundary layer in the space, thereby forming a spatial steady-state turbulent field.

[0037] Specifically, when the soap film layer 6 flows, the nylon rope 5 will be stretched toward the soap film layer 6 under the action of surface tension, forming a curved distribution. The flow channel will be displaced when the soap film layer 6 flows relative to the flow channel without the soap film layer 6, causing the soap film layer 6 to accelerate first and then decelerate in the experimental section, which seriously affects the flow channel performance. Through theoretical analysis, it is found that the displacement generated by each nylon rope 5 is Where γ is the surface tension of the soap film 6, m is the weight of a single weight 9, and Figure 1 , X2 is the length of the experimental section in the figure.

[0038] Specifically, the minimum weight of weight 9 is Where γ is the surface tension of the soap film layer 6, X2 is the length of the experimental section, δ y The maximum allowable shrinkage distance of the nylon rope 5.

[0039] Specifically, a peristaltic pump 15 is provided in the reflux channel 10 to send the liquid in the lower water tank 3 into the upper water tank 2 through the peristaltic pump 15 for reciprocating circulation. At the same time, the average speed of the soap film layer 6 can be adjusted by adjusting the flow rate of the peristaltic pump 15.

[0040] The control method of the two-dimensional water tunnel experimental device specifically includes the following steps:

[0041] (1) The soap liquid in the upper water tank 2 flows out through the nozzle 4, forming a soap film layer 6 between the nylon ropes 5 on both sides;

[0042] (2) The front and rear glass plates 7 are rotated around the fixed ends respectively, and the movable ends of the front and rear glass plates 7 are opened to form the soap film layer 6 to adjust the space;

[0043] (3) The tracer particles 11 in the soap film layer 6 are illuminated by a pulsed laser, and two high-speed cameras 13 take pictures of the tracer particles 11 facing them. When the tracer particles 11 fall on the camera focus plane with a depth of field of only 23 μm, the tracer particles 11 are clearly imaged. Otherwise, the tracer particles 11 are out of focus. Based on the images, the four hooks 8 are continuously adjusted until all the tracer particles 11 are clearly imaged, indicating that the plane formed by the four hooks 8 coincides with the camera focus plane, that is, the soap film layer 6 is in the same plane;

[0044] (4) Rotate the front and rear glass plates 7 around the fixed ends respectively, and move the movable ends of the front and rear glass plates 7 closer to each other until the glass plates 7 are parallel to the soap film layer 6;

[0045] (5) The soap liquid flows into the lower water tank 3 and is sent into the upper water tank 2 by the peristaltic pump 15.

[0046] The above-mentioned two-dimensional water tunnel experimental device is used in various fluid mechanics experiments.

[0047] Working principle of the present invention:

[0048] During the experimental preparation stage, the front and rear glass plates 7 are rotated around the fixed ends respectively so that the moving ends of the front and rear glass plates 7 are separated from each other to facilitate the subsequent debugging of the soap film layer 6. The soap liquid flows out of the upper water tank 2 along the nozzle 4. At the outlet of the nozzle 4, the two nylon ropes 5 form a gradually expanding plane, where the soap liquid gradually expands to form a soap film layer 6. With the continuous acceleration of gravity, it reaches full development in the experimental section and finally flows into the lower water tank 3. It is sent into the upper water tank 2 along the reflux channel 10 by the peristaltic pump 15, forming a reciprocating cycle. At the same time, the tracer particles 11 in the soap film layer 6 are illuminated by a pulsed laser. Two high-speed cameras 13 photograph the facing tracer particles 11. Combined with the images, the four hooks 8 are continuously adjusted until the four hooks 8 are located in the same plane to ensure that the soap film layer 6 is in the same plane. Finally, the front and rear glass plates 7 are rotated around the fixed ends respectively so that the moving ends of the front and rear glass plates 7 are close to each other until the glass plates 7 and the soap film layer 6 are parallel to each other, and the experiment is carried out.

[0049] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A two-dimensional water tunnel experimental device, characterized by: The invention comprises a first bracket (1), an upper water tank (2) and a lower water tank (3), wherein the bottom of the upper water tank (2) is connected to a nozzle (4), and the outlet of the nozzle (4) is connected to two nylon ropes (5), a soap film layer (6) is formed between the nylon ropes (5) on both sides, and glass plates (7) are respectively provided on the front and rear sides of the soap film layer (6), and hooks (8) are respectively provided between the upper and lower sides of the two nylon ropes (5) and the adjacent first brackets (1), and weights (9) are hung on the lower ends of the nylon ropes (5), and the weights (9) are immersed in the lower water tank (3), and a reflux channel (10) is provided between the upper water tank (2) and the lower water tank (3); the first bracket (1) is provided with at least one hinge (14), and any side of the glass plates (7) on the front and rear sides is connected through the hinge (14) ) is hinged, and after the glass plates (7) on both sides are closed, the glass plates (7) are respectively located on both sides of the soap film layer (6) and are parallel to the soap film layer (6); the two-dimensional water tunnel experimental device also includes a second bracket (16) arranged parallel to the first bracket (1); the second bracket (16) is fixedly provided with a grid (12) and a high-speed camera (13), the grid (12) vertically passes through the upstream position of the soap film layer (6), and two high-speed cameras (13) arranged in sequence along the flow direction are arranged in parallel on the outside of the downstream position of the soap film layer (6); a peristaltic pump (15) is provided in the reflux channel (10); the soap film layer (6) includes 2% dishwashing liquid, 10% glycerol and 88% deionized water by mass, and the soap film layer (6) is added with tracer particles (11).

2. A two-dimensional water tunnel experimental device according to claim 1, characterized in that: When the soap film layer (6) flows, due to the effect of surface tension, the displacement of each nylon rope (5) toward the inside of the soap film layer (6) is ,in is the surface tension of the soap film layer (6), is the weight of a single weight (9), is the length of the experimental section.

3. A two-dimensional water tunnel experimental device according to claim 2, characterized in that: The minimum weight of the single weight (9) is ,in is the maximum displacement of each nylon rope (5) toward the inner side of the soap film layer (6).

4. A control method for a two-dimensional water tunnel experimental device according to claim 1, characterized in that: The specific steps include: (1) The soap liquid in the upper water tank (2) flows out through the nozzle (4) to form the soap film layer (6) between the nylon ropes (5) on both sides; (2) rotating the glass plates (7) on the front and rear sides around the fixed ends respectively, and opening the movable ends of the glass plates (7) on the front and rear sides to form a soap film layer (6) to adjust the space; (3) The tracer particles (11) in the soap film layer (6) are illuminated by a pulsed laser, and the two high-speed cameras (13) take pictures of the tracer particles (11) facing each other. When the tracer particles (11) fall within a depth of field of only If the camera focuses on the plane, the tracer particles (11) are clearly imaged. Otherwise, the tracer particles (11) are out of focus. In combination with the image, the four hooks (8) are continuously adjusted until all the tracer particles (11) are clearly imaged. This indicates that the plane formed by the four hooks (8) coincides with the camera focus plane, that is, the soap film layer (6) is in the same plane; (4) rotating the front and rear glass plates (7) around the fixed ends respectively, and moving the front and rear glass plates (7) closer to each other until the glass plates (7) on both sides are parallel to the soap film layer (6); (5) The soap film layer (6) flows into the lower water tank (3) and is sent into the upper water tank (2) by the peristaltic pump (15).

5. A two-dimensional water tunnel experimental device as claimed in claim 1 is used in various fluid mechanics experiments.

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