A water tunnel experimental device, system and method based on the principle of ejection

Abstract

The application discloses a water tunnel experimental device, system and method based on an ejecting principle, and belongs to the technical research field of hydrodynamic experiments; the experimental device comprises a front return flow section, an experimental section, a static section, a rear return flow section, a bottom fairing section and a power system; the front return flow section, the experimental section, the rear return flow section and the bottom fairing section are sequentially connected through flanges to form a closed water tunnel; the static section is a pipeline with open ends and is connected in parallel with the experimental section, one end of the static section is connected to an outlet end of the front return flow section, and the other end of the static section is connected to an inlet end of the rear return flow section; the power system is used for moving fluid; when high-speed fluid flowing from the front return flow section enters the experimental section, the high-speed fluid is in contact with fluid in the static section to generate momentum exchange; the high-speed fluid drives low-speed fluid in the static section to move, so that a low Reynolds number flow space is formed in the experimental section.

Description

Technical Field

[0001] This invention belongs to the field of hydrodynamic experimental technology research, specifically involving a water tunnel experimental device, system and method based on the ejection principle, and provides a cyclic, freely adjustable water tunnel experimental platform that can achieve low Reynolds number and low turbulence. Background Technology

[0002] Flow problems around bluff bodies are widespread in aerospace and marine engineering fields, such as the support structures of airfoils, cooling towers, and offshore platforms. The flow field around these bluff body structures involves a variety of flow phenomena, such as flow separation, vortex generation, and vortex shedding. Among these, the alternating vortex shedding from both sides of the bluff body causes it to experience significant drag and lift. When the bluff body is elastically connected, if the vortex shedding frequency is close to the system's natural frequency, vortex-induced vibration can be induced. When a structure is under vortex-induced vibration, it can further lead to fatigue and failure.

[0003] Experimental methods are crucial for exploring the aforementioned hydrodynamic problems, and designing a high-performance experimental setup is a prerequisite for effectively acquiring this flow information. Water tunnels are a common and effective experimental device in hydrodynamics research. Based on a pre-defined pipeline, a power unit generates adjustable water flow, simulating the interaction between the experimental object and the water flow field within the test section for experimental research. Unlike models moving in still water, in water tunnel experiments, the experimental model is stationary, and the experimental setup controls the relative velocity by manipulating the water flow. Current water tunnel setups can be classified into two types based on their structure: The first is the vertical water tunnel, powered by gravity, which forces water into the test section at a certain velocity without requiring an additional power system; it is also known as a gravity-driven water tunnel. The second is the circulating water tunnel, powered by a water pump, which propels the water flow in a reciprocating cycle within the pipeline. Circulating water tunnels are often equipped with a control system to manipulate the flow velocity and pressure within the pipe, making them a sealed experimental device for collecting and processing data during high-speed flow. Because gravity-type water tunnels occupy a large space and the flow velocity in the test section is related to the water level, which is not conducive to control and observation, circulation-type water tunnels are often used.

[0004] Existing water tunnel experimental systems mostly employ designs with large channels, high flow rates, and high velocities. Long-term operation under such conditions not only causes wear and tear on the test section, contraction section, and expansion section, but also, due to their structural characteristics, only allows for hydrodynamic studies at high Reynolds numbers (generally, a Reynolds number greater than 3900 is considered high), making fundamental hydrodynamic studies at low Reynolds numbers impossible. For example, the Chinese patent "A Low-Disturbance, High-Flow Rate High-Speed ​​Circulating Water Tunnel Experimental System" describes a water tunnel experimental system with advantages such as a large cross-sectional area of ​​the test section, high flow velocity and flow rate, and low frictional disturbance. Another example is the Chinese patent "Vertical Pressure-Adjustable Temperature Experimental Water Tunnel," which is easy to disassemble and move, and can simulate flow fields under different temperatures, depths, pressures, and velocities. Neither of these patents describes water tunnel experimental devices suitable for conducting fundamental hydrodynamic studies at low Reynolds numbers.

[0005] Currently, numerical methods, namely "direct numerical simulation," can solve relatively realistic flow field environments. Numerical simulations are quite accurate for Reynolds numbers below approximately 1000. However, for Reynolds numbers greater than 1000, accurate solutions obtained through direct numerical simulation require significant time investment. Using Reynolds-averaged methods or large eddy simulations introduces additional errors. Experiments at low Reynolds numbers, on the other hand, can better couple the experimental and numerical simulation results. Furthermore, effective active flow control measures can be developed at low Reynolds numbers to reduce drag and vibration. Since the current mainstream approach is to use numerical simulations to solve for active flow control at Reynolds numbers of 100-1000, experiments at low Reynolds numbers (100-1000) are necessary to verify the feasibility of these flow control measures. However, current circulating water tunnels, when studying bluff body flow problems, typically operate at Reynolds numbers around 7000, making low Reynolds number experiments impossible. Therefore, we propose a circulating water tunnel device suitable for low Reynolds numbers. Summary of the Invention

[0006] The technical problem to be solved:

[0007] To overcome the shortcomings of existing technologies, this invention provides a water tunnel experimental device, system, and method based on the ejection principle. A pre-recirculation section, an experimental section 6, a post-recirculation section, and a bottom rectifying section are sequentially connected via flanges to form a closed water tunnel. By connecting a stationary section 5 in parallel to the experimental section, with the contraction sections of the pre-recirculation section and the post-recirculation section connected to its two ends respectively, the fluid velocity in the experimental section 6 is reduced based on the ejection principle without adding additional disturbance. This provides an experimental environment with low Reynolds number and low turbulence, suitable for observing and measuring relevant hydrodynamic parameters at lower Reynolds numbers. The water tunnel experimental device of this invention has a small footprint, simple structure, and compact design. The experimental observation section experiences minimal disturbance along the flow path, and the water flow velocity is low and stable.

[0008] The technical solution of the present invention is: a water tunnel experimental device based on the ejection principle, comprising a pre-return section, an experimental section 6, a stationary section 5, a post-return section, a bottom rectification section and a power system, wherein the pre-return section, the experimental section, the post-return section and the bottom rectification section are connected in sequence by flanges to form a closed water tunnel;

[0009] The stationary section 5 is a pipe open at both ends, connected in parallel with the experimental section 6. One end of it is connected to the outlet of the pre-recirculation section, and the other end is connected to the inlet of the post-recirculation section. The fluid is moved by the power system. When the high-speed fluid flowing in from the pre-recirculation section enters the experimental section 6, it comes into contact with the fluid in the stationary section 5 and generates momentum exchange. The high-speed fluid will drive the low-speed fluid in the stationary section 5 to move, thereby forming a low Reynolds number flow space in the experimental section 6.

[0010] A further technical solution of the present invention is as follows: the pre-recirculation section includes a pre-bending section and a contraction section connected in sequence, with a total length of L1; the post-recirculation section includes an expansion section, a transition section 10, and a post-bending section connected in sequence, with a total length of L2, wherein L1 > L2; the bottom rectification section includes a power section 13 and a rectification section 17 connected in sequence; the cross-sections of the pre-bending section, transition section, post-bending section, and bottom rectification section are circular, with a cross-sectional area of ​​S1; the cross-section of the experimental section 6 is circular, with a cross-sectional area of ​​S2; the cross-section of the contraction section is circular, with a contraction angle between 5° and 10°; the cross-section of the expansion section is circular, with an expansion angle between 8° and 12°; the contraction section realizes the transition from S1 to S2, and the expansion section realizes the transition from S2 to S1;

[0011] The upper side wall of the power section 13 is provided with a water inlet 14. The power section 13 is equipped with a power system, which consists of a motor 15 and a propeller 16. The motor 15 and the propeller 16 are connected by a coupling. The rectifier section 17 is equipped with a pressure and flow regulation system 19 for regulating the flow rate and internal pressure. The side wall of the rectifier section 17 is provided with a water outlet 18.

[0012] A further technical solution of the present invention is: the shrinking section includes a first shrinking section 1, a second shrinking section 3, and a third shrinking section 4 with an end radius ratio of 4:3:2. The first shrinking section 1, the second shrinking section 3, and the third shrinking section 4 are arranged coaxially in sequence and connected to each other by a flange; the specific position where the stationary section 5 enters the shrinking section is at the third shrinking section 4.

[0013] The expansion section includes a first expansion section 7 and a second expansion section 8, which are arranged sequentially and connected by a flange; the end radius ratio of the first expansion section 7, the second expansion section 8 and the transition section 10 is 1:2:4; the specific location where the stationary section 5 enters the expansion section is the first expansion section 7.

[0014] A further technical solution of the present invention is: a first rectifier mesh 2 is installed in the first contraction section 1, a second rectifier mesh 9 is installed inside the transition section 10, and a rectifier 20 is installed inside the rectifier section 17 near the front bending section; the rectifier 20 is a multi-layer fine rectifier mesh, and the mesh surface of the fine rectifier mesh is covered with a plurality of small cylindrical holes with a diameter of 8mm.

[0015] A further technical solution of the present invention is: the experimental section 6 is divided into two regions, the one near the contraction section is the mixing and deceleration section 61, in which the fluid is mixed and decelerated; the one near the expansion section is the experimental observation section 62, in which a low Reynolds number flow space is formed; the inner wall of the experimental observation section 62 is connected to a flow meter 24 and a pressure sensor 25 for water tunnel measurement and control.

[0016] A further technical solution of the present invention is as follows: the front bending section includes a first bending section 21 and a second bending section 22, and the rear bending section includes a third bending section 11 and a fourth bending section 12; the bending angles of the first bending section 21, the second bending section 22, the third bending section 11, and the fourth bending section 12 are all 90°; the first bending section 21 and the second bending section 22 are connected by a flange, and the third bending section 11 and the fourth bending section 12 are connected by a flange; the horizontal section, contraction section, experimental section 6, expansion section, transition section 10 of the second bending section 22, and the horizontal section of the third bending section 11 are all coaxial; the horizontal section, bottom rectifying section, and horizontal section of the first bending section 21 and the fourth bending section 12 are all coaxial.

[0017] A further technical solution of the present invention is that: a flow guiding device is installed inside the first bending section 21, the second bending section 22, the third bending section 11, and the fourth bending section 12 to reduce the impact loss of the fluid.

[0018] A further technical solution of the present invention is: a pressure regulating valve 51 is installed in the middle of the stationary section 5.

[0019] An experimental system using a water tunnel experimental apparatus based on the ejection principle includes the ejection principle-based water tunnel experimental apparatus, a laser 28, a synchronizer 27, a computer 29, and a high-speed camera 30. The laser 28 is equipped with an optical arm 26, the light source of which is located above the experimental observation section 62. The high-speed camera 30 is used to acquire photographs of the fluid in the experimental observation section 62. The synchronizer 27 is connected to the laser 28 and is used to synchronize the laser 28 and the high-speed camera 30. The computer 29 is connected to the synchronizer 27, the laser 28, the high-speed camera 30, and the motor 15, and is used to control the motor 15, the high-speed camera 30, the synchronizer 27, and the laser 28, as well as to collect and process the data transmitted by the high-speed camera 30.

[0020] An operating method for the aforementioned experimental system, comprising the following specific steps:

[0021] Step 1: Fill the water tunnel experimental device with water, add an appropriate amount of PIV special tracer particles when filling the water, and adjust the pressure and flow regulation system 19 until the water is full;

[0022] Step 2: Start the experimental system and activate the circulating water tunnel device to ensure that the PIV-specific tracer particles and water are fully mixed in the rectifier 20;

[0023] Step 3: Install the blunt body 23 inside the experimental observation section 62, and illuminate the tracer particles on the plane with the sheet light source 31 generated by the laser;

[0024] Step 4: The movement of tracer particles in experimental observation section 62 is interpreted as the movement of fluid. The movement process of tracer particles is collected by high-speed camera 30, and the collected information is transmitted to computer 29 for processing.

[0025] Step 5: Process the data using computer 29 to obtain the low Reynolds number data of the experiment, which is used to verify the results obtained from the direct numerical simulation in computer 29.

[0026] Beneficial effects

[0027] The beneficial effects of this invention are as follows: This invention provides a water tunnel experimental device based on the ejection principle. A stationary section is connected in parallel to the experimental section, with a contraction section and an expansion section connected to both ends of the stationary section. The fluid flowing into the experimental section from the pre-return section has a high velocity. When it enters the mixing and deceleration section, the velocity fluid and the stationary fluid connected to the contraction section of the stationary section undergo shearing. Due to the intermolecular forces within the fluid, this shearing hinders the fluid's acceleration. Therefore, under the action of viscous forces, the velocity fluid interacts with the stationary fluid, generating momentum exchange and forming a stable low-velocity flow in the central axis region of the experimental section pipe. This results in a high-quality flow space with low Reynolds number, low turbulence, and low disturbance in the experimental observation section. The low Reynolds number circulating water tunnel described in this invention, by adjusting the motor speed, can maintain the flow velocity in the observation section at 10 mm / s, making it more suitable for the mechanistic study of bluff body wakes and ensuring that the flow field non-uniformity is less than 3%.

[0028] The contraction section of this invention consists of three segments. The contraction angle of these segments can be changed according to specific experimental requirements, thus achieving a wider range of velocity variations. By setting the contraction angle between 5° and 10°, a suitable fluid velocity can be effectively guaranteed, resulting in better shearing effects between the velocifying fluid and the stationary fluid. Each segment of the contraction section is connected by a standard flange, making it more economical. The gradually changing contraction section effectively reduces disturbances and energy losses caused by abrupt changes in cross-section, ensuring that the velocity vector is in the same direction when the fluid flows into the experimental section. Under low Reynolds number conditions, this contraction section design can also effectively reduce the initial power input.

[0029] This invention uses a variable frequency motor connected to a propeller to input power. When the input power needs to be changed, the variable frequency motor can stably change the current flow field environment, avoiding the extra disturbances caused by traditional flow valve design. At the same time, the rotation of the propeller can reduce the initial turbulence intensity to a certain extent, which is beneficial to providing a good initial environment for the entire experimental system and can achieve stepless speed change in the speed range of 0.01m / s to 1.0m / s.

[0030] The experimental observation section of this invention can be equipped with a particle image velocimetry (PIV) experimental measurement device and a model pulsating pressure measurement device according to specific requirements. This part has strong overall adaptability. Since it is in a low Reynolds number experimental environment, the experimental data can be coupled with the data from high-fidelity direct numerical simulation to explore fluid-related mechanistic issues.

[0031] The experimental apparatus of this invention can be installed vertically or horizontally. In vertical installation, it saves space and is convenient to equip with other measurement systems. The components of this invention are easy to install and disassemble, and are easy to manufacture. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the overall structure of the water tunnel experimental device based on the ejection principle described in this invention;

[0033] Figure 2 This is a schematic diagram illustrating the principle of the experimental section described in this invention;

[0034] Figure 3 Schematic diagram of the experimental system described in this invention;

[0035] Figure 4 This is a schematic diagram of the contraction segment described in this invention;

[0036] Figure 5 This is a schematic diagram of the expansion section described in this invention.

[0037] Explanation of reference numerals in the attached diagram: 1. First contraction section 2. First rectifier network 3. Second contraction section 4. Third contraction section 5. Stationary section 5. Regulating valve 5. Stationary section pipeline 6. Experimental section 6. Mixing deceleration section 6. Experimental observation section 7. First expansion section 8. Second expansion section 9. Second rectifier network 10. Transition section 11. Third bend section 12. Fourth bend section 13. Power section 14. Inlet 15. Motor 16. Propeller 17. Rectifier section 18. Outlet 19. Pressure and flow regulation system 20. Rectifier 21. First bend section 22. Second bend section 23. Blunt body 24. Flow meter 25. Pressure sensor 26. Optical arm 27. Synchronizer 28. Laser 29. Computer 30. High-speed camera 31. Sheet light source. Detailed Implementation

[0038] The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the invention, and should not be construed as limiting the invention.

[0039] See Figure 1 This invention discloses a water tunnel experimental device based on the ejection principle, comprising a first curved section 21, a second curved section 22, a first contraction section 1, a second contraction section 3, a third contraction section 4, an experimental section 6, a first expansion section 7, a second expansion section 8, a transition section 10, a third curved section 11, a fourth curved section 12, a power section 13, and a rectifying section 17 connected sequentially by flanges, forming a closed water tunnel. The water tunnel experimental device is vertically arranged, with a total height of 1600mm and a total width of 3370mm. The experimental observation section 62 is 1500mm above the bottom, facilitating close-range observation and adjustment.

[0040] See Figure 1 The water tunnel experimental device also includes a stationary section 5, which includes a pressure regulating valve 51 and a stationary section pipeline 52. The stationary section pipeline 52 is open at both ends, with one end connected to the third contraction section 4 and the other end connected to the first expansion section 7. The pressure regulating valve 51 is installed in the middle of the stationary section pipeline 52 to regulate the fluid pressure in the stationary section pipeline 52. The stationary section 5 is connected in parallel with the experimental section 6.

[0041] See Figure 1 The power section 13 has a circular inlet 14 on its upper side wall, and the rectifier section 17 has a circular outlet 18 on its side wall. The rectifier section 17 is equipped with a pressure and flow regulation system 19 for regulating flow rate and internal pressure. The power section 13 is equipped with a motor 15 and a propeller 16. The motor 15 is a variable frequency motor, which is connected to the propeller 16 via a coupling. The variable frequency motor drives the propeller 16 to move the fluid. Before the velocity fluid enters the inlet of the experimental section 6, it will come into contact with the fluid in the stationary section 5 connected to the third contraction section 4. The velocity fluid and the stationary fluid will undergo shearing. Due to the intermolecular interaction forces within the fluid, the acceleration of the fluid will be hindered. Therefore, under the action of viscous forces, the velocity fluid will interact with the stationary fluid, resulting in momentum exchange. The high-speed fluid will drive the low-speed fluid in the stationary section 5 to move, thereby forming a low Reynolds number flow space in the experimental section 6.

[0042] See Figure 1In this invention, the cross-sections of the first bending section 21, the second bending section 22, the transition section 10, the third bending section 11, the fourth bending section 12, the power section 13, and the rectifier section 17 are all circular with an inner diameter of 400 mm. The wall thickness of each bending section is 10 mm. The power section 13 and the rectifier section 17 are of equal length, both 950 mm. The experimental section 6 has a circular cross-section with a diameter of 100 mm. The bending angles of the first bending section 21, the second bending section 22, the third bending section 11, and the fourth bending section 12 are all 90°. Guide vanes are installed inside each of the four bending sections to alleviate the centrifugal force of the fluid turning and reduce impact loss.

[0043] See Figure 1 , Figure 4 The first contraction section 1, the second contraction section 3, and the third contraction section 4 have circular cross-sections, and each contraction section has the same length of 320 mm. The ratio of the end radii of the first contraction section 1, the second contraction section 3, and the third contraction section 4 is 4:3:2. The maximum inner diameter of the first contraction section 1 is 400 mm. The total contraction angle of each contraction section is between 5° and 10°, which is conducive to the uniform increase of fluid velocity, thereby reducing the turbulence in the incoming flow.

[0044] See Figure 1 , Figure 5 The first expansion section 7 and the second expansion section 8 have circular cross-sections, and the total length of the two expansion sections is 520 mm. The ratio of the end radii of the first expansion section 7, the second expansion section 8, and the transition section 10 is 1:2:4. The minimum diameter of the first expansion section 7 is 100 mm. The ratio of the two end radii of the first expansion section 7 is 1:2, and the ratio of the two end radii of the second expansion section 8 is 2:4. The transition section 10 is a straight hole, which serves to connect the second expansion section 8 and the third curved section 11. When the fluid flows out of the experimental section 6, it will still have a certain velocity. In order to effectively reduce the outflow velocity, according to the law of conservation of mass, a larger expansion angle is required. Therefore, the total expansion angle of the expansion sections is designed to be between 8° and 12°. In this invention, the total length of the first curved section 21, the second curved section 22, the first contraction section 1, the second contraction section 3, and the third contraction section 4 is 1460 mm, and the total length of the first expansion section 7, the second expansion section 8, the transition section 10, the third curved section 11, and the fourth curved section 12 is 1260 mm.

[0045] See Figure 1 The horizontal sections of the second curved section 22, the first contraction section 1, the second contraction section 3, the third contraction section 4, the experimental section 6, the first expansion section 7, the second expansion section 8, the transition section 10, and the horizontal sections of the third curved section 11 are all coaxial; the horizontal sections of the first curved section 21, the rectifying section 17, the power section 13, and the horizontal sections of the fourth curved section 12 are all coaxial.

[0046] See Figure 1The first contraction section 1 is equipped with a first rectifier net 2 to break up eddies in the water flow introduced by the first bend section 21 and the second bend section 22, thereby ensuring the flow field quality of the incoming flow to the contraction section. The transition section 10 is equipped with a second rectifier net 9 to reduce turbulence in the fluid. The rectifier section 17 is equipped with a rectifier 20 near the first bend section 21. The rectifier 20 is a multi-layer fine rectifier net with multiple small cylindrical holes of 8mm diameter on its surface. The rectifier 20 breaks up eddies formed in the velocity fluid, thereby reducing the turbulence of the fluid entering the first bend section 21. To reduce the pulsating force caused by fluid velocity fluctuations, a pressure and flow regulating valve 19 is positioned before the rectifier net 20, i.e., near the power section 13. This invention, by installing rectifier nets or rectifiers of different specifications inside the first contraction section 1, the transition section 10, and the rectifier section 17, can reduce the instability of fluid flow and provide a good initial environment for the entire experimental system.

[0047] See Figure 1 , Figure 2 The experimental section 6 of this invention is divided into two regions: a mixing and deceleration section 61 near the third contraction section 4, where the incoming flow undergoes mixing and deceleration; and an experimental observation section 62 near the first expansion section 7, where a low Reynolds number flow space is formed, and the test model bluff body 23 is installed in the experimental observation section. The Reynolds number is defined as Re = ρvd / μ, where ρ is the fluid density, v is the fluid velocity, d is the characteristic length, and μ is the viscosity coefficient. When the size of the object being tested is fixed, to ensure a low Reynolds number, the flow velocity in the experimental observation section 62 needs to be reduced. This invention effectively reduces the incoming flow velocity through the mixing and deceleration section 61, reducing the velocity of the fluid flowing in from the third contraction section 4. With a relatively high velocity, when it enters the mixing and deceleration section 61 and comes into contact with the fluid in the stationary section 5, momentum exchange occurs. The high-speed fluid drives the low-speed fluid in the stationary section 5, thus forming a low Reynolds number flow space in the central axis region of the experimental observation section 62. This is particularly suitable for observing and measuring relevant hydrodynamic parameters under low Reynolds number and low turbulence conditions. The experimental observation section 62 can be customized according to different experimental needs. If visualization experiments are required, this section can be made of high-strength, optically resistant plexiglass to facilitate close-range observation or particle image velocimetry (PIV) measurements. If it is necessary to measure the pressure on the experimental model, a pressure sensor can be installed on the surface or inside the test model, with leads extending from the top of the experimental section for measurement and monitoring. The inner wall of the experimental observation section 62 is connected to a flow meter 24 and a pressure sensor 25 for flow and pressure measurement and control. The total length of the experimental observation section 62 is 300 mm, and its diameter is 100 mm.

[0048] The experimental testing process of the water tunnel experimental device based on the ejection principle of this invention is as follows:

[0049] Step 1: Open the inlet 14 to inject water into the circulating water tunnel device, and adjust the pressure and flow regulation system 19 until the device is full of water;

[0050] Step 2: Start the variable frequency motor. The variable frequency motor drives the propeller 16 to rotate at low speed, and the fluid inside the pipe moves accordingly.

[0051] Step 3: The accelerated fluid passes through the rectifier section 17, where the irregular vortex structure is broken by the dense cylindrical holes of the rectifier 20, thereby reducing the turbulence of the fluid entering the first curved section 21.

[0052] Step 4: After the regular fluid rectified by rectifier 20 passes through the curved section 22, it may bring new interference. Therefore, a first rectifier net 2 is installed in the first contraction section 1 to reduce the disturbance. The fluid passes through the first contraction section 1, the second contraction section 3, and the third contraction section 4, which will cause it to shear the fluid in the stationary section 5 at a higher speed.

[0053] Step 5: The high-speed incoming flow interacts with the low-speed fluid in stationary section 5. Based on the ejection principle, the high-speed incoming flow will decelerate in the mixing and deceleration section 61, thereby forming a flow field environment with low Reynolds number and low turbulence in experimental observation section 62.

[0054] Step Six: Adjust the output power of the variable frequency motor according to the experimental requirements so that the fluid in the experimental observation section 62 reaches the required flow velocity, thereby enabling experimental observation of the test model installed in the experimental observation section 62.

[0055] Step 7: After observing the completed fluid flow through the first expansion section 7 and the second expansion section 8, since the expansion angle of the expansion section is greater than the contraction angle of the contraction section, the fluid velocity will decrease more quickly to avoid impacting the third bending section 11 and the fourth bending section 12.

[0056] See Figure 3If more refined experiments are required on the water tunnel experimental device based on the ejection principle described in this invention, such as observing the wake of a blunt body, the formation and shedding of a Karman vortex street, and vortex-induced vibrations, a particle image velocimetry (PIV) experimental measurement device can be added to measure fluid-related dynamic parameters. Based on this, this invention proposes an experimental system using a water tunnel experimental device based on the ejection principle. This system includes the aforementioned water tunnel experimental device, a laser 28, a synchronizer 27, a computer 29, and a high-speed camera 30. The laser 28 has an optical arm 26, with the light source of the optical arm 26 located above the experimental observation section 62. The high-speed camera 30 is used to acquire photographs of the fluid in the experimental observation section 62. The synchronizer 27 is connected to the laser 28 to synchronize the triggering of the laser 28 and the high-speed camera 30. The computer 29 is connected to the synchronizer 27, the laser 28, the high-speed camera 30, and the motor 15, and is used to control the motor 15, the high-speed camera 30, the synchronizer 27, and the laser 28, as well as to collect and process the data transmitted by the high-speed camera 30.

[0057] The specific implementation steps of using the experimental system described in this invention are as follows:

[0058] Step 1: Fill the water tunnel experimental device with water. When filling the water, add an appropriate amount of PIV special tracer particles. The sphericity of the tracer particles is >95%, and the main chemical composition is SiO2 >65%. Adjust the pressure and flow rate regulation system 19 until the water is full.

[0059] Step 2: Start the experimental system and activate the circulating water tunnel device to ensure that the PIV-specific tracer particles and water are fully mixed in the rectifier 20;

[0060] Step 3: Install the blunt body 23 inside the experimental observation section 62. The laser 28 is model MGL-N-532A-4W. Adjust the optical arm 26 to find a suitable observation surface. Adjust the laser intensity. The sheet light source 31 generated by the laser 28 illuminates the tracer particles on the plane.

[0061] Step 4: The movement of tracer particles in experimental observation section 62 is interpreted as the movement of fluid. The movement process of tracer particles is collected by high-speed camera 30, and the collected information is transmitted to computer 29 for processing.

[0062] In the fifth step, computer 29 uses the "cross-correlation algorithm" to process the collected information and obtain the low Reynolds number data of the experiment, which is used to verify the results of the direct numerical simulation in the computer.

[0063] The flow environment around a bluff body at low Reynolds numbers exhibits strong periodicity, making it highly suitable for fundamental research in hydrodynamics and allowing for the exploration of mechanistic problems. Existing numerical simulation techniques offer high accuracy in solving low Reynolds number environments, and this water tunnel experimental setup can effectively couple experimental data with numerical simulation techniques.

[0064] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A water tunnel experimental apparatus based on the principle of ejection, characterized in that: It includes a pre-recirculation section, an experimental section (6), a stationary section (5), a post-recirculation section, a bottom rectification section, and a power system. The pre-recirculation section, the experimental section, the post-recirculation section, and the bottom rectification section are connected in sequence by flanges to form a closed water tunnel. The stationary section (5) is a pipe with open ends, connected in parallel with the experimental section (6). One end of it is connected to the outlet end of the pre-recirculation section, and the other end is connected to the inlet end of the post-recirculation section. The fluid is moved by the power system. When the high-speed fluid flowing in from the pre-recirculation section enters the experimental section (6), it comes into contact with the fluid in the stationary section (5) and generates momentum exchange. The high-speed fluid will drive the low-speed fluid in the stationary section (5) to move, thereby forming a low Reynolds number flow space in the experimental section (6).

2. The water tunnel experimental apparatus based on the ejection principle according to claim 1, characterized in that: The pre-recirculation section includes a pre-bending section and a contraction section connected in sequence, with a total length of L1; the post-recirculation section includes an expansion section, a transition section (10) and a post-bending section connected in sequence, with a total length of L2, where L1 > L2; the bottom rectification section includes a power section (13) and a rectification section (17) connected in sequence; the cross-sections of the pre-bending section, transition section, post-bending section and bottom rectification section are circular, with a cross-sectional area of ​​S1; the cross-section of the experimental section (6) is circular, with a cross-sectional area of ​​S2; the cross-section of the contraction section is circular, with a contraction angle between 5° and 10°; the cross-section of the expansion section is circular, with an expansion angle between 8° and 12°; the contraction section realizes the transition from S1 to S2, and the expansion section realizes the transition from S2 to S1; The upper side wall of the power section (13) is provided with an inlet (14). The power section (13) is equipped with a power system, which consists of a motor (15) and a propeller (16). The motor (15) and the propeller (16) are connected by a coupling. The rectifier section (17) is equipped with a pressure and flow regulation system (19) for regulating the flow rate and internal pressure. The side wall of the rectifier section (17) is provided with an outlet (18).

3. The water tunnel experimental apparatus based on the ejection principle according to claim 2, characterized in that: The contraction section includes a first contraction section (1), a second contraction section (3), and a third contraction section (4) with an end radius ratio of 4:3:

2. The first contraction section (1), the second contraction section (3), and the third contraction section (4) are arranged coaxially in sequence and connected by flanges. The specific location where the stationary section (5) is connected to the pre-return section is in the third contraction section (4). The expansion section includes a first expansion section (7) and a second expansion section (8), which are arranged in sequence and connected by a flange; the ratio of the end radii of the first expansion section (7), the second expansion section (8) and the transition section (10) is 1:2:4; the specific location where the stationary section (5) is connected to the post-return section is the first expansion section (7).

4. The water tunnel experimental apparatus based on the ejection principle according to claim 3, characterized in that: The first contraction section (1) is equipped with a first rectifier mesh (2), the transition section (10) is equipped with a second rectifier mesh (9), and the rectifier section (17) is equipped with a rectifier (20) near the front bending section. The rectifier (20) is a multi-layer fine rectifier mesh, and the mesh surface of the fine rectifier mesh is covered with multiple small cylindrical holes with a diameter of 8mm.

5. The water tunnel experimental apparatus based on the ejection principle according to claim 2, characterized in that: The experimental section (6) is divided into two regions: a mixing and deceleration section (61) near the contraction section, where the fluid is mixed and decelerated; and an experimental observation section (62) near the expansion section, where a low Reynolds number flow space is formed. The inner wall of the experimental observation section (62) is connected to a flow meter (24) and a pressure sensor (25) for water tunnel measurement and control.

6. The water tunnel experimental apparatus based on the ejection principle according to claim 2, characterized in that: The pre-bending section includes a first bending section (21) and a second bending section (22), and the post-bending section includes a third bending section (11) and a fourth bending section (12); the bending angles of the first bending section (21), the second bending section (22), the third bending section (11), and the fourth bending section (12) are all 90°. The first bending section (21) and the second bending section (22) are connected by a flange, and the third bending section (11) and the fourth bending section (12) are connected by a flange; the horizontal section, contraction section, experimental section (6), expansion section, transition section (10) of the second bending section (22) and the horizontal section of the third bending section (11) are all coaxial, and the horizontal section, bottom rectification section, and horizontal section of the first bending section (21) and the fourth bending section (12) are all coaxial.

7. The water tunnel experimental apparatus based on the ejection principle according to claim 6, characterized in that: The first curved section (21), the second curved section (22), the third curved section (11), and the fourth curved section (12) are equipped with flow guiding devices to reduce the impact loss of the fluid.

8. The water tunnel experimental apparatus based on the ejection principle according to claim 1, characterized in that: A pressure regulating valve (51) is installed in the middle of the stationary section (5).

9. An experimental system for a water tunnel experimental apparatus based on the ejection principle as described in claim 1, characterized in that: The device includes the water tunnel experimental apparatus based on the ejection principle, a laser (28), a synchronizer (27), a computer (29), and a high-speed camera (30). The laser (28) is equipped with an optical arm (26), and the light source of the optical arm (26) is located above the experimental observation section (62). The high-speed camera (30) is used to collect photographs of the fluid in the experimental observation section (62). The synchronizer (27) is connected to the laser (28) and is used to synchronize the laser (28) and the high-speed camera (30). The computer (29) is connected to the synchronizer (27), the laser (28), the high-speed camera (30), and the motor (15) and is used to control the motor (15), the high-speed camera (30), the synchronizer (27), and the laser (28), as well as to collect and process the data transmitted by the high-speed camera (30).

10. A method for operating the experimental system of claim 9, characterized in that, The specific implementation steps are as follows: Step 1: Fill the water tunnel experimental device with water, add an appropriate amount of PIV special tracer particles when filling the water, and adjust the pressure and flow regulation system (19) until the water is full; Step 2: Start the experimental system and start the circulating water tunnel device to fully mix the PIV-specific tracer particles with water in the rectifier (20); Step 3: Install the blunt body (23) inside the experimental observation section (62), find a suitable observation surface, and use the sheet light source (31) generated by the laser to illuminate the tracer particles on the surface; Step 4: The movement process of tracer particles in the experimental observation section (62) is collected by a high-speed camera (30), and the collected information is transmitted to a computer (29) for processing; Step 5: The low Reynolds number data of the experiment are obtained by processing the data through a computer (29) to verify the results of the direct numerical simulation in the computer (29).

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