Three-dimensional experimental device and method for measuring transient flow field of gravity flow in real time

Abstract

The invention discloses a three-dimensional experimental device and method for measuring a gravity flow transient flow field in real time. The inflow diffusion system is composed of a water inlet hose and diffusers, diffusers of different structures are adopted for plume and density flow, and therefore uniform and stable inflow conditions are created; the terrain simulation system comprises an experiment water tank, an overflow pool and a terrain obstacle, and it is fully guaranteed that stable inflow can be supplied for a long time in the water tank with the finite length. The flow field observation system is divided into a laser surface making module, a data recording module and a structure supporting module, and quasi-three-dimensional multi-angle measurement is carried out on the flow process of plume and density flow by configuring PIV system equipment at different positions. By arranging the diffuser and combining the PIV technology with the electric sliding rail, the evolutionary process of plume / density current flowing through complex natural terrains / engineering objects in the actual situation is reproduced through simple operation, and the flowing process of snow melting plume flowing through the bottom of an iceberg can be simulated.

Description

Technical Field

[0001] The present invention belongs to the field of hydrodynamic research, and particularly relates to a three-dimensional experimental device and method for real-time measurement of the transient flow field of gravity currents. Background Art

[0002] Gravity current refers to the shear flow phenomenon that occurs between fluids with density differences, and is usually divided into density currents and plumes according to the difference between the density of the inflow fluid and the density of the ambient fluid. Gravity currents widely exist in natural environments such as the deep sea and rivers, and are common in natural phenomena such as continental shelf landslides, riverbed sediment deposition, and glacier melting, often causing great damage to underwater topography and engineering structures. However, due to the very complex interaction mechanism between gravity currents and natural topography and engineering structures during their movement, coupled with their suddenness, randomness, large scale, and the characteristic of being difficult to measure in real time, the field research on gravity currents has always been lacking.

[0003] The flume experiment has always been a classic method for studying the dynamics of gravity currents. In the published patent solutions, there are already various flume systems for gate-opening two-dimensional gravity currents at home and abroad. However, in nature, the large scale of gravity currents in the spatial scale and the continuity in the time scale both mean that it is more in line with the flow characteristics of continuously inflowing three-dimensional gravity currents. However, due to the complex structure of the device, high cost, and the complexity and difficulty of the implementation method, the existing experimental devices have the following limitations: they focus more on two-dimensional experiments and rarely on three-dimensional experiments; overall, they focus on gate-opening gravity currents and lack research on continuously inflowing gravity currents; the devices are usually only applicable to density currents and cannot take into account both density currents and plumes. Therefore, there is an urgent need to design a three-dimensional continuously inflowing gravity current experimental device with low cost and able to ensure uniformity, so as to better understand the turbulent characteristics and flow state evolution of gravity currents during the flow process, and provide more data support for field observations and numerical simulations. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the present invention provides a three-dimensional experimental device and method for real-time measurement of the transient flow field of gravity currents, aiming to make up for the defect that it is difficult to manufacture and measure a stable and continuously inflowing gravity current in traditional gravity current experiments. Through modular processing of the equipment in different regions, the experimental device can conveniently realize real-time three-dimensional measurement of the interaction process of continuously inflowing density currents, plumes and three-dimensional obstacles, and has strong versatility on the premise of streamlining the structure, which can greatly reduce the difficulty and complexity of three-dimensional density current laboratory experiments.

[0005] To solve the above technical problems, the technical solutions adopted by the present invention are as follows: In the first aspect of the present invention, there is provided a three-dimensional experimental device for real-time measurement of the transient flow field of gravity currents, and the device includes: An inflow diffusion system, used to generate uniform and stable inflow conditions, includes an inlet hose and a diffuser. The diffuser can be a plume diffuser or a density current diffuser according to experimental requirements. A terrain simulation system, used to simulate natural terrain or engineering structures, includes an experimental flume and replaceable terrain obstacles. A flow field observation system, used to perform quasi-three-dimensional multi-angle measurement on the flow process of gravity current, includes a laser, a high-speed camera and a controller. The laser and the high-speed camera are set on a slide rail and connected to the controller, and can achieve automatic movement and data acquisition.

[0006] On the other hand, the present invention provides a method for real-time measuring the transient flow field of gravity current by using a three-dimensional experimental device, including the following steps: Step a. Set up the experimental environment, including selecting and fixing the corresponding terrain obstacles and diffusers. Step b. Prepare the inflow fluid and the ambient water body, ensuring that their densities are different but their refractive indices are the same. Step c. Start the inflow diffusion system, and make the inflow fluid uniformly diffuse into the experimental flume through the diffuser. Step d. Start the flow field observation system, and record the flow field data through the laser and the high-speed camera. Step e. Use a densitometer to measure the water body density in real time, and analyze it in combination with the flow field data. Step f. By changing the experimental conditions, including the fluid density and the obstacle shape, repeat the above steps to obtain multiple sets of data.

[0007] The beneficial effects of the present invention are as follows: 1. The facilities of the present invention are simple, the process is easy, the layout is flexible, the cost is low, and the main measurement method is non-invasive. Therefore, the experimental results have good reliability, accuracy and usability.

[0008] 2. By matching different devices, the present invention can manufacture and measure two different gravity currents, namely plume and density current. By setting an automatic circulation program for the electric slide rail in the flow field observation system, two-dimensional flow field profile data at multiple different positions can be recorded in one experiment, so as to quickly obtain a quasi-three-dimensional flow field. Combining the condition that the present invention can measure the vertical profile and the horizontal profile along the flow direction respectively, the flow field data in the x-y-z three directions can be obtained, so as to realize the three-dimensional real-time measurement of the flow field of three-dimensional continuous inflow type gravity current.

[0009] 3. The two diffusers described in the present invention disperse and weaken the kinetic energy in a single direction by allowing the point-source inflow fluid to enter the inflow cavity first, and then accumulate the fluid in the inflow cavity until the inflow cavity is filled and then overflows from the outlet port that is uniform and dense in the span direction, thereby ensuring that the point-source inflow fluid can be evenly diffused into the experimental water tank along the span direction. This structure does not require customized wide-sized inflow water pipes and high-power water pumps even when conducting experiments in larger and wider water tanks. Only small-sized water pumps and universal water pipes are needed to supply water to the water tank, which greatly simplifies the complex requirements of traditional three-dimensional continuous inflow experiments on water supply devices.

[0010] 4. The present invention can measure the gravity flow field with a large density difference by using different light-heavy solution combinations. In the heterogeneous flow experiment, potassium dihydrogen phosphate aqueous solution-glycerol solution was used; in the plume experiment, ethanol solution-sodium chloride solution was used.

[0011] 5. When the present invention is used in a density flow experiment, a smooth reflector is used to make the laser emitted obliquely upward by the laser below reflect and illuminate the obstacle. Through the principle of mirror refraction, the radiation range of the laser surface is expanded, and flow field information in a wider range can be recorded.

[0012] 6. By setting up an overflow tank to receive the environmental water overflowing from the experimental flume due to inflow, it is possible to ensure that a quasi-constant inflow is maintained for as long as possible in a flume of limited length.

[0013] 7. Obstacles of various shapes, sizes, and materials can be used to simulate different types of actual terrain, natural materials, man-made objects, etc. in the real environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the front view of the device of the present invention; Figure 2 is a schematic top view of the device of the present invention; Figure 3 yes Figure 1 Schematic diagram of replaceable parts; Figure 4 yes Figure 2 Schematic diagram of replaceable parts; Figure 5 It is a schematic diagram of the diffuser structure and the corresponding controller; Figure 6 It is a schematic diagram of horizontal profile velocity.

[0015] In the figure: 1, inlet hose; 2, plume diffuser; 3, experimental water tank; 4, laser; 5, bottom slide rail; 6, overflow pool; 7, obstacle; 8, movable support; 9, densitometer; 10, high-speed camera; 11, side slide rail; 12, density current diffuser; 13, smooth reflector; 14, plume inflow chamber; 15, plume outflow chamber; 16, plume water inlet; 17, plume water outlet; 18, density current inflow chamber; 19, density current outflow chamber; 20, density current water inlet; 21, density current water outlet; 22, upper slide rail; 23, controller. Detailed implementation manners

[0016] In the present invention, unless otherwise clearly specified and defined, terms such as "arranged" and "connected" shall be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the internal communication of two components or the interaction relationship between two components, unless otherwise clearly defined. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0017] The following are only some embodiments of the present invention, which do not limit the patent scope of the present invention. Any equivalent structural transformation made by using the content of the specification of the present invention, or directly or indirectly applied to the technical fields of other related products, is included in the patent protection scope of the present invention.

[0018] This application provides a three-dimensional experimental device for real-time measurement of the transient flow field of gravity flow, which is mainly divided into three parts: an inflow diffusion system, a terrain simulation system, and a flow field observation system.

[0019] The flow field observation system mainly consists of a laser 4, a densitometer 9, a high-speed camera 10, a bottom slide rail 5, a side slide rail 11, and an upper slide rail 22. The bottom slide rail 5, the side slide rail 11, and the upper slide rail 22 are synchronously controlled by a controller 23. The densitometers 9 are evenly arranged upstream, downstream, and laterally of an obstacle 7 used to simulate natural terrain or artificial structures for measuring the real-time density at different positions. The laser 4 and the high-speed camera 10 are mounted on different slide rails. By using the high-speed camera 10 to photograph the laser profile formed by the irradiation of the laser 4, the unit displacement of the tracer particles in the inflow fluid is obtained, so as to obtain the velocity field.

[0020] Furthermore, for the flow field observation system described above, the electric slide rail can be automatically operated through the program settings of the controller. By setting the same cyclic program of moving fixed distance - stationary fixed time - restarting moving fixed distance - restarting stationary fixed time for the two slide rails respectively, the laser 4 and the high-speed camera 10 can move together, and under the condition of maintaining an appropriate focal length, two-dimensional flow field profile data at multiple different positions can be automatically recorded, so as to obtain a quasi-three-dimensional flow field.

[0021] Preferably, the slide rail should have various motion modes (such as directional motion, timed restart, etc.), and the motion speed is in the range of 0 - 20 cm / s.

[0022] Preferably, the laser uses a continuous-wave neodymium-doped yttrium aluminum garnet (Nd:YAG Laser) light source with a wavelength of 532 nm and a power setting of 11 W. A Powell prism with a refraction angle of 30° is placed at the outlet of the light source. After the laser is refracted by the prism, a laser plane with a thickness of about 4 mm is formed, and the position is adjusted to ensure that the obstacle is located in the center of the laser plane.

[0023] Preferably, the exposure time of each frame of the high-speed camera is 3000 μs, the acquisition frame rate is controlled at 190 Hz, and the shooting duration of the high-speed camera for each group of experiments is 80 s.

[0024] Preferably, the tracer particles of the experimental device are polystyrene with a particle size of 50 μm and a density of 1.04 g / cm 3 , to ensure the clarity of the particles in the obtained PIV images.

[0025] The inflow diffusion system mainly consists of an inlet water hose 1, a plume diffuser 2 or a density current diffuser 12, and an overflow tank 6. Inside the plume diffuser, the plume enters the plume inflow chamber 14 in the plume diffuser 2 through the inlet water hose 1 from the plume inlet 16, and flows out from the plume outlet 17 after passing through the plume outflow chamber 15; inside the density current diffuser 12, the fluid enters the density current inflow chamber 18 in the density current diffuser 12 through the inlet water hose 1 from the density current inlet 20, and flows out from the density current outlet 21 after passing through the density current outflow chamber 19. The diffuser can make the fluid of the point-source inflow uniformly diffuse along the span direction, thus ensuring the uniformity of the inflow fluid in the three-dimensional experiment.

[0026] The terrain simulation system mainly consists of an experimental water tank 3, a replaceable terrain obstacle 7, and a movable support 8.

[0027] Preferably, to ensure that the spanwise scale meets the requirements of three-dimensional experiments and eliminate the wall effect, the width of the experimental water tank should be more than 4 times the spanwise length of the obstacle, and the height of the experimental water tank should be more than 4 times the height of the obstacle. The length of the experimental water tank should be not less than 300 cm to ensure the persistence of the quasi-steady region of the inflow fluid. The experimental water tank is made of transparent acrylic board to ensure its good light transmission performance.

[0028] Preferably, the obstacle should be made of photosensitive resin and painted black to avoid the influence of the reflection on the surface of the obstacle on the recording of the movement of nearby PIV particles as much as possible.

[0029] In one embodiment, Figure 1 Region A in [Figure number] is the inflow region in the front view, and the replaceable component is Figure 3 in (a) of [Figure number]; Figure 1 Region B in [Figure number] is the observation region in the front view, and the replaceable component is Figure 3 in (b), (c), and (d) of [Figure number]; Figure 1 In [Figure number], the positive x-axis direction is the horizontal direction along the flow direction, the y-axis direction is the horizontal direction along the spanwise direction, and the positive z-axis direction is the vertical direction same as the direction of the gravitational acceleration.

[0030] Figure 2 Region C in [Figure number] is the observation region in the top view, and the replaceable component is Figure 4 in (e) of [Figure number].

[0031] Figure 5 In [Figure number], the upper left is the plume diffuser, the lower left is the density current diffuser, and the right side is the schematic diagram of the controller.

[0032] Furthermore, when conducting experiments on the interaction between the plume and the terrain, Figure 1 the equipment in Region A in [Figure number] remains unchanged. Among them, the plume diffuser 2 is placed near the water surface on the right side of the experimental water tank 3, and the upper edge of the plume outlet 17 is flush with the water surface; the obstacle 7 is installed on the movable bracket 8, and the bottom is flush with the water surface.

[0033] When conducting experiments on the interaction between the density current and the terrain, Figure 1 the equipment in Region A in [Figure number] is replaced with Figure 3 in (a) of [Figure number], which consists of the water inlet hose 1 and the density current diffuser 12. The density current diffuser 12 is placed at the bottom on the right side of the experimental water tank 3, and the lower edge of the density current outlet 21 is flush with the bottom of the experimental water tank 3; the obstacle 7 is installed at the bottom of the experimental water tank 3.

[0034] Furthermore, when measuring the flow field of the x-y section, Figure 1 the equipment in Region C in [Figure number] is replaced with Figure 4 in (e) of [Figure number], that is, the laser is installed on the side slide rail 11 on the side of the experimental water tank 3, and a horizontal laser section is created through the side wall of the experimental water tank 3.

[0035] When measuring the plume, the equipment in area B in Figure 1 needs to be replaced with the one in Figure 3 , that is, the high-speed camera 10 is fixed on the bottom slide rail 5 under the experimental water tank 3; When measuring the density current, the equipment in area B in Figure 1 needs to be replaced with the one in Figure 3 , that is, the high-speed camera 10 is fixed on the upper slide rail 22 on the movable support 8.

[0036] Furthermore, when measuring the flow field of the x-z cross-section, area C remains unchanged. For the plume, Figure 1 the equipment in area B in Figure 1 does not need to be changed, that is, the laser 4 is installed on the bottom slide rail 5 under the experimental water tank 3, and a laser profile is created upward through the transparent bottom of the water tank. The high-speed camera 10 is installed on the side slide rail 11 on the side of the experimental water tank 3; for the density current, the area A in Figure 3 needs to be changed to Figure 1 in Figure 3 , that is, the laser 4 irradiates upward from the side lower part of the experimental water tank 3 onto the smooth mirror 13, and after reflection, a laser profile is formed at the required position.

[0037] Summarize as follows: (1) When recording the flow field of the x-y cross-section in the experiment of the interaction between the plume and the terrain, the laser profiling module consists of a laser and a side slide rail, the data recording module consists of a densitometer, a high-speed camera, and a lower slide rail, and the structural support module consists of a movable support and a controller, that is, the default components in area A and components (c) (e) are used; (2) When recording the flow field of the x-z cross-section in the experiment of the interaction between the plume and the terrain, the laser profiling module consists of a laser and a lower slide rail, the data recording module consists of a densitometer, a high-speed camera, and a side slide rail, and the structural support module consists of a movable support and a controller, that is, the default components in areas A, B, and C are used; (3) When recording the flow field of the x-y cross-section in the experiment of the interaction between the density current and the terrain, the laser profiling module consists of a laser and a side slide rail, the data recording module consists of a densitometer, a high-speed camera, and an upper slide rail, and the structural support module consists of a movable support and a controller, that is, components (a) (d) (e) are used; (4) When recording the flow field of the x-z cross-section in the experiment of the interaction between the density current and the terrain, the laser profiling module consists of a laser, a lower slide rail, and a smooth mirror, the data recording module consists of a densitometer, a high-speed camera, and a side slide rail, and the structural support module consists of a movable support and a controller, that is, components (a) (b) and the default components in area C are used.

[0038] Furthermore, when used in a heterogeneous flow experiment, a smooth reflector 13 is installed at a suitable angle on the movable bracket 8 so that the laser light emitted obliquely upward by the laser 4 below is reflected onto the obstacle 7. Based on the principle of mirror refraction, the radiation range of the laser surface is expanded and flow field information in a larger range is recorded.

[0039] Furthermore, under the premise of ensuring the consistency of refractive index and obtaining clear flow field images, different light-heavy solution combinations are used according to the refractive index change curve of different solute solutions with density to maximize the density difference between the ambient water body and the plume / hyperdensity flow. In the hyperdensity flow experiment, potassium dihydrogen phosphate solution-propylene glycol solution is preferably used; in the plume experiment, ethanol solution-sodium chloride solution is preferably used.

[0040] Furthermore, by providing an overflow pool 6 for receiving the environmental water overflowing from the experimental water tank 3 due to the inflow, it is possible to ensure that a quasi-constant inflow is maintained for as long as possible in the water tank of limited length.

[0041] The present application also provides a method for real-time measurement of the transient flow field of gravity flow using the three-dimensional experimental device, which specifically comprises the following steps: a. Set up the actual terrain environment, inflow diffusion system and observation system. According to the different experimental fluids, select and fix the corresponding obstacles and diffusers, and select the corresponding devices for layout according to the required measurement profile.

[0042] The controller 23 is used to initially set the movement speed, movement distance, dwell interval and number of repetitions of the laser slide rail 5, and the laser slide rail 5 is powered on to move. The movement of the laser surface is observed to determine the movement stability of the laser 4, and then the controller 23 is turned off. According to the specific experimental requirements, the density meter 9 is evenly arranged upstream, downstream and to the side of the obstacle 7, and is connected to the control system in advance for calibration to ensure its measurement accuracy.

[0043] b. Preparation of inflow fluid ρ 1 and environmental water bodies 2 . In the experiment of plume and topography, the environmental water body is a colorless high-density solution, and the inflow fluid entering the experimental water tank 3 from the water inlet hose 1 is a colorless low-density solution with tracer particles. In the experiment of heterogeneous flow and topography, the environmental water body is a colorless low-density solution, and the inflow fluid entering the experimental water tank 3 from the water inlet hose 1 is a colorless high-density solution with tracer particles. In the experiment, it is necessary to ensure that the solute density of the environmental water body and the inflow fluid is different, but the refractive index is consistent. When the environmental water fills the experimental water tank, it is necessary to ensure that the inside of the diffuser is also filled with environmental water.

[0044] c. Open the slide rails for the laser and the camera, the laser 4, and the high-speed camera 10. After confirming that the movement mode is appropriate, first start the switch of the water inlet hose 1 to let the incoming water body enter the experimental water tank 3. Open the densitometer 9 to record the density of the water body. After the main part of the incoming water body enters the laser section, turn on the controller 23 to let the laser 4 and the high-speed camera 10 start recording the multi-layer PIV images. After the experiment, through the calibration of the image size and the actual size using the PIVLAB program in MATLAB, quantitative vertical and horizontal flow states of the gravity current, fluid thickness, displacement distance, velocity field, vorticity field, etc. can be obtained by methods such as image cross-correlation, and subsequent processing and analysis can be carried out.

[0045] d. Repeat the above experimental steps, and conduct multiple groups of experiments by changing the density of the ambient fluid and the incoming fluid, the shape and size of the obstacle 7, etc., to obtain rich experimental data on the interaction between the density current and the plume and the obstacle.

[0046] Verification example: To verify the spanwise uniformity of the horizontal velocity distribution in the flow process of the three-dimensional continuous incoming plume manufactured by the plume diffuser, select the default components in regions A, B, and C in the figure and add them to the experimental device to obtain the x-z cross-sectional flow field of the plume.

[0047] In this example, the rectangular transparent water tank is made of acrylic, with a width of 70 cm, a total length of 400 cm, and a depth of 70 cm. Among them, the length of the overflow area is 70 cm. The internal width of the diffuser is 69 cm, the length is 10 cm, the height is 10 cm, and the diameter of a single water outlet is 1.4 cm.

[0048] The high-speed camera used is a CCD camera, with a maximum resolution of 2592×2048 pixels and a field of view of approximately 25 cm×21 cm; the wavelength of the laser used is 532 nm, the power is 11 W, and the divergence angle is 30°. The high-speed camera and the laser are installed 130 cm away from the right wall surface. The obstacle is removed, and glycerol solution is used as the incoming fluid and potassium dihydrogen phosphate solution is used as the ambient water body for refractive index matching.

[0049] In this example, the experimental steps taken are as follows: Step 1. Arrange the required experimental device and prepare the corresponding solutions. Add the ambient water body to the experimental water tank and reach the required depth of 40 cm.

[0050] Step 2. Set the initial positions of the laser and the high-speed camera at 35 cm along the y-direction, i.e., at the midpoint. Set the motion program of the electric slide rail through the controller to stop for 4 seconds every 1 cm after startup, repeat 4 times, and then change to stop for 4 seconds every 2 cm and repeat 2 times to record the flow field profiles at seven positions of 0, 1, 2, 3, 4, 6, and 8 cm from the midpoint. At the same time, check whether the slide rail and various measuring devices are operating normally.

[0051] Step 3. Open the switch of the inlet hose to let the inflowing fluid enter the diffuser at a flow rate of 1.054×10 -3 m 3 / s. When the fluid passing through the laser profile reaches a quasi-steady state, start the PIV measurement system to record data, and start the controller program to change the laser profile position after 4 seconds.

[0052] Step 4. Post-process the obtained results. The horizontal profile velocity is as Figure 6 shown. Figure 6 In (a), it is the time-averaged horizontal velocity gradient curve of the seven profiles. Figure 6 In (b), it is the horizontal velocity gradient curves of the upstream, middle, and downstream. Figure 6 In (c), it is the laser profile, i.e., the horizontal velocity gradient curve of the plume at the midpoint at different times. The above results verify from two perspectives of space and time that the velocity gradient of the plume can maintain a quasi-steady state during the flow process. It can be seen that the experimental device proposed by the present invention can effectively generate a stable three-dimensional continuous inflow gravity flow and be used to conduct corresponding obstacle experiments.

[0053] The above content is a further detailed description of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention belongs, without departing from the concept of the present invention, several simple deductions or substitutions can still be made, and all should be regarded as belonging to the protection scope of the present invention.

Claims

1. A three-dimensional experimental device for real-time measurement of transient flow field of gravity flow, characterized in that: The device comprises: An inflow diffusion system, used to generate uniform and stable inflow conditions, comprising a water inlet hose (1) and a diffuser, wherein the diffuser is a plume diffuser (2) or a density flow diffuser (12) selected according to experimental requirements; A terrain simulation system for simulating natural terrain or engineered structures, including an experimental flume (3) and replaceable terrain obstacles (7); A flow field observation system is used for performing quasi-three-dimensional multi-angle measurement on the flow process of a gravity flow, comprising a laser (4), a high-speed camera (10) and a controller (23); the laser (4) and the high-speed camera (10) are arranged on a slide rail and connected to the controller (23), and can realize automatic movement and data collection.

2. The three-dimensional experimental device for real-time measurement of transient flow field of gravity flow according to claim 1 is characterized in that: The flow field observation system also includes a densitometer (9), which is evenly arranged upstream, downstream and to the side of the terrain obstacle (7) and is used to measure the density of water bodies at different locations in real time.

3. The three-dimensional experimental device for real-time measurement of transient flow field of gravity flow according to claim 1 is characterized in that: The diffuser in the inflow diffusion system is used to diffuse the fluid inflow from a point source uniformly along the span direction.

4. The three-dimensional experimental device for real-time measurement of transient flow field of gravity flow according to claim 1 is characterized in that: The laser (4) and the high-speed camera (10) in the flow field observation system are synchronously controlled by a controller (23) and can automatically record two-dimensional flow field profile data at multiple different positions according to a preset motion program, thereby obtaining quasi-three-dimensional flow field information.

5. The three-dimensional experimental device for real-time measurement of transient flow field of gravity flow according to claim 1 is characterized in that: The device also includes a smooth reflecting mirror (13) which is used to expand the radiation range of the laser surface by reflecting laser light in a density flow experiment, thereby recording flow field information in a larger range.

6. The three-dimensional experimental device for real-time measurement of transient flow field of gravity flow according to claim 1 is characterized in that: The experimental water tank (3) is made of transparent acrylic material to ensure good light transmission performance, and the width of the water tank is more than 4 times the span length of the obstacle, the height is more than 4 times the height of the obstacle, and the length is not less than 300 cm.

7. The three-dimensional experimental device for real-time measurement of transient flow field of gravity flow according to claim 1 is characterized in that: The device is provided with an overflow pool (6) to receive the environmental water overflowing from the experimental water tank (3) due to the inflow, so as to maintain a quasi-constant inflow for a relatively long time.

8. A method for real-time measurement of transient flow field of gravity flow using the three-dimensional experimental device according to any one of claims 1 to 7, characterized in that: The following steps are involved: Step a. Setting up the experimental environment, including selecting and fixing corresponding terrain obstacles (7) and diffusers; Step b. preparing the inflow fluid and the ambient water to ensure that the two have different densities but the same refractive index; Step c. starting the inflow diffusion system to allow the inflow fluid to diffuse evenly through the diffuser into the experimental water tank (3); Step d. starting the flow field observation system to record the flow field data through the laser (4) and the high-speed camera (10); Step e. Using a densitometer (9) to measure the water density in real time, and analyzing it in combination with the flow field data; Step f. Repeat the above steps to obtain multiple sets of data by changing the experimental conditions, including fluid density and obstacle shape.

9. The method for real-time measurement of transient flow field of gravity flow according to claim 8, characterized in that: In step b, for the plume experiment, a low-density solution with tracer particles is used as the inflow fluid, and a high-density solution is used as the ambient water body; for the heterogeneous flow experiment, a high-density solution with tracer particles is used as the inflow fluid, and a low-density solution is used as the ambient water body.

10. The method for real-time measurement of transient flow field of gravity flow according to claim 8, characterized in that: In step e, the flow field data is processed by an image cross-correlation method to obtain quantitative velocity field and vorticity field to analyze the flow characteristics of the gravity flow.

Images