Experimental device and method for particle transport based on artificial upwelling

Abstract

The present invention discloses an experimental device and method for transporting particles based on artificial upwelling, comprising a transparent water tank; an upwelling generating unit is used for forming a stable upwelling in the transparent water tank; a particle releasing container is used for adding particles into the upwelling generating unit so that the particles enter the transparent water tank together with the upwelling; a circulating flow generating unit is used for generating a cross flow in the transparent water tank; a shooting unit is used for shooting movement and diffusion images of particles, which can better simulate the movement and diffusion process of particles entrained by the artificial upwelling, and provide a low-cost experimental research platform for theoretical calculation, numerical simulation and practical engineering application.

Description

Technical Field

[0001] The present application relates to the field of artificial upwelling research, and specifically to a particle transport experimental device and method based on artificial upwelling. Background Art

[0002] In recent years, marine artificial upwelling technology is a geoengineering method that, by placing artificial systems to form seawater flow from the seabed to the sea surface, can lift particulate waste and use the action of tides to transport it to the open sea outside the aquaculture area, reducing the organic load in the aquaculture area and thus improving the ecological environment of the aquaculture area.

[0003] In order to study the particle transport mechanism based on artificial upwelling, it is necessary to clarify the movement and diffusion process of particles entrained by artificial upwelling. However, there is currently no relevant equipment and device that can simulate and observe it. Therefore, it is urgent to propose an experimental device that can be used to explore the movement of particles entrained by artificial upwelling. Summary of the invention

[0004] In view of this, the embodiments of the present application provide a particle transport experimental device and method based on artificial upwelling to simulate the movement and diffusion process of particles entrained by artificial upwelling, providing a convenient and low-cost experimental research platform for theoretical calculations, numerical simulations and practical engineering applications.

[0005] The technical solution adopted by the present invention is as follows:

[0006] In a first aspect, a particle transport experimental device based on artificial upwelling is provided, comprising:

[0007] Transparent sink;

[0008] An upflow generating unit is used to form a stable upflow in the transparent water tank, and the upflow generating unit comprises: a liquid storage container, a peristaltic pump, a liquid replenishment container, a separation container, and a nozzle which are sequentially connected through pipelines, wherein the liquid storage container contains saline and tracer required for the experiment, and the peristaltic pump continuously supplies liquid to the liquid replenishment container so that the separation container is in an overflow state during the experiment, and the saline and tracer in the separation container are discharged from the nozzle;

[0009] a particle release container, which adds particles into the rehydration container so that the particles enter the transparent water tank along with the upflow;

[0010] A circulation flow generating unit, used for generating a cross flow in the transparent water tank; and

[0011] The shooting unit is used to shoot the movement and diffusion images of particles.

[0012] Optionally, the upflow generating unit further includes an upper valve and a lower valve, wherein the upper valve is arranged on the pipeline between the liquid replenishing container and the separation container, and the lower valve is arranged on the pipeline between the separation container and the nozzle.

[0013] Optionally, the particle release container, the liquid replenishment container and the separation container are fixed on the bracket from top to bottom by a clamp.

[0014] Optionally, the upflow generating unit further comprises an overflow collecting container for collecting liquid overflowing from the separation container, and the overflow channel at the upper end of the separation container is connected to the overflow collecting container via a pipeline.

[0015] Optionally, the nozzle is J-shaped, with the longer vertical section and horizontal section respectively fixed to the side wall and bottom of the transparent water tank, and the shorter vertical section fixed to the vertical center plane along the flow direction in the transparent water tank.

[0016] Optionally, the circulating flow-generating unit includes a rectifying component, a connecting pipe, a water pump, a flow meter and a flow-generating controller. The rectifying component is installed upstream of the transparent water tank. Both ends of the connecting pipe are connected to the bottom of both ends of the transparent water tank. The water pump and the flow meter are arranged on the connecting pipe. The water pump and the flow meter are electrically connected to the flow-generating controller.

[0017] Optionally, the shooting unit includes a computer, a synchronizer, a laser power supply, a laser, a light sheet and a high-speed camera, wherein the synchronizer input end is electrically connected to the computer, and the output end is electrically connected to the laser power supply and the high-speed camera respectively; the high-speed camera is electrically connected to the computer; the laser is connected to the laser power supply; the light sheet is installed at the output end of the laser; the light sheet is arranged above the nozzle outlet, the high-speed camera is placed directly in front of the side wall of the transparent water tank, and the high-speed camera lens is aimed at the nozzle outlet area.

[0018] In a second aspect, a particle transport experimental method based on artificial upwelling is provided, the method is implemented in the particle transport experimental device based on artificial upwelling described in the first aspect, the method comprising:

[0019] S1: Add tracer to saline and store it in a storage container, and place particles in a particle release container;

[0020] S2: According to the initial rising flow velocity required by the experiment, adjust the height of the separation container and exhaust the channel between the separation container and the nozzle outlet: open the upper valve and the lower valve, start the peristaltic pump, inject salt water into the separation container, wait for the nozzle outlet to start discharging salt water, and then close the lower valve and the peristaltic pump;

[0021] S3: Inject tap water into the transparent water tank to the experimental water depth. According to the cross-flow speed required by the experiment, set the flow rate in the transparent water tank through the flow controller, and the water pump will automatically adjust the speed to make the flow rate reach the set value; turn on the peristaltic pump and continue to inject salt water into the separation container until its water level reaches the overflow surface and maintains the overflow state; open the lower valve, and the salt water in the separation container is discharged from the nozzle and enters the environmental water body in the transparent water tank. Since the separation container always maintains the overflow state, a stable upwelling is formed; observe the flow development process of the upwelling through the tracer, and after it is fully developed, open the particle release container. At this time, the particles in the particle release container enter the rehydration container under the action of gravity, and then enter the transparent water tank from the nozzle outlet together with the upwelling;

[0022] S4: The synchronizer is controlled by a computer, which enables the laser power supply and the high-speed camera to work synchronously. While the sheet light source generates laser sheet light to illuminate the particles, the high-speed camera takes pictures and uploads the captured motion and diffusion images of the particles to the computer.

[0023] The technical solution provided by the embodiments of the present application may have the following beneficial effects:

[0024] It can be seen from the above embodiments that the upwelling generating unit of the present invention is used to form a stable upwelling in the transparent water tank, the particle releasing container is used to add particulate matter into the upwelling generating unit so that the particulate matter enters the transparent water tank together with the upwelling, the circulating flow generating unit is used to generate a cross flow in the transparent water tank, and the shooting unit is used to shoot the movement and diffusion images of the particulate matter, which can better simulate the movement and diffusion process of the particulate matter entrained by the artificial upwelling, and provide a low-cost experimental research platform for theoretical calculations, numerical simulations and practical engineering applications.

[0025] In the present invention, the height difference ∆H between the overflow surface of the separation container and the water level in the transparent water tank is changed by adjusting the height of the separation container, so as to obtain the initial rising flow velocity required for the experiment at the nozzle outlet. This method can obtain a continuous initial rising flow velocity within a certain range and can better adapt to changes in experimental conditions.

[0026] In the present invention, the flow rate in the transparent water tank is set by a flow controller, and the water pump will automatically adjust the speed to make the flow rate reach the set value, so that a continuous cross-flow speed within a certain range can be obtained, which can better adapt to changes in experimental conditions.

[0027] The present invention can replace nozzles within a certain diameter range, and can better adapt to changes in experimental conditions.

[0028] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0030] Figure 1 It is a schematic structural diagram of a particle transport experimental device based on artificial upwelling according to an embodiment of the present invention.

[0031] Figure 2 Schematic diagram of water flow direction of a particle transport experimental device based on artificial upwelling in an embodiment of the present invention.

[0032] Figure 3 Schematic diagram of a nozzle fixing method of a particle transport experimental device based on artificial upwelling in an embodiment of the present invention.

[0033] The reference numerals in the figures are:

[0034] 10. Transparent sink;

[0035] 20. Upflow generating unit; 21. Liquid storage container; 22. Peristaltic pump; 23. Liquid replenishing container; 24. Separation container; 25. Sprinkler; 26. Upper valve; 27. Lower valve; 28. Overflow collection container;

[0036] 30. Particle release container;

[0037] 40. Circulation flow generating unit; 41. Rectification component; 42. Connecting pipe; 43. Water pump; 44. Flow meter; 45. Flow generating controller;

[0038] 50. Shooting unit; 51. Computer; 52. Synchronizer; 53. Laser power supply; 54. Laser; 55. Light source; 56. High-speed camera

[0039] 60. Bracket. DETAILED DESCRIPTION

[0040] Exemplary embodiments will be described in detail herein, examples of which are shown in the accompanying drawings. When the following description refers to the drawings, the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The implementations described in the following exemplary embodiments do not represent all implementations consistent with the present application. Instead, they are merely examples of devices and methods consistent with some aspects of the present application as detailed in the appended claims.

[0041] The terms used in this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The singular forms of "a", "said" and "the" used in this application and the appended claims are also intended to include plural forms unless the context clearly indicates other meanings. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more associated listed items.

[0042] refer to Figure 1-Figure 3 The embodiment of the present invention provides a particle transport experimental device based on artificial upwelling, which may include: a transparent water tank 10, an upwelling generating unit 20, a particle release container 30, a circulation flow generating unit 40 and a shooting unit 50. The upwelling generating unit 20 is used to form a stable upwelling in the transparent water tank 10; the particle release container 30 is used to add particles to the upwelling generating unit 20 so that the particles enter the transparent water tank 10 together with the upwelling; the circulation flow generating unit 40 is used to generate a cross flow in the transparent water tank 10; the shooting unit 50 is used to shoot the movement and diffusion images of particles. The device can better simulate the movement and diffusion process of particles entrained by artificial upwelling, and provide a low-cost experimental research platform for theoretical calculation, numerical simulation and practical engineering application.

[0043] In one embodiment, the upflow generating unit 20 is used to form a stable upflow in the transparent water tank 10; the upflow generating unit 20 comprises: a liquid storage container 21, a peristaltic pump 22, a liquid replenishment container 23, a separation container 24, and a nozzle 25 connected in sequence through pipelines, and the particle release container 30 adds particles to the liquid replenishment container 23. The liquid storage container 21 contains saline and tracer required for the experiment, and the peristaltic pump 22 continuously supplies liquid to the liquid replenishment container 23, so that the separation container 24 is in an overflow state during the experiment.

[0044] The upflow generating unit 20 further includes an upper valve 26 and a lower valve 27, wherein the upper valve 26 is disposed on the pipeline between the liquid replenishing container 23 and the separation container 24, and the lower valve 27 is disposed on the pipeline between the separation container 24 and the nozzle 25. The upper valve 26 and the lower valve 27 are used to control the discharge of liquid from the liquid replenishing container 23 and the separation container 24, respectively, so that a sufficient flow of liquid can be provided during the experiment to fill the pipeline between the separation container 24 and the outlet of the J-shaped nozzle 25.

[0045] Specifically, the particle release container 30, the rehydration container 23 and the separation container 24 are fixed on the bracket from top to bottom by a clamp. The bracket can be placed next to the transparent water tank 10; the inlet of the peristaltic pump 22 is connected to the liquid storage container 21 through a hose, and the outlet is connected to the rehydration container 23 through a hose; the outlet below the rehydration container 23 is connected to one end of the upper valve 26 through a hose, and the other end of the upper valve 26 is aligned with the upper opening of the separation container 24; the overflow channel at the upper end of the separation container 24 is connected to the overflow collection container 28 through a hose, and the outlet at the lower end is connected to one end of the lower valve 27 through a hose, and the other end of the lower valve 27 is connected to the inlet of the nozzle 25 through a hose.

[0046] In order to collect the liquid overflowing from the separation container 24, the upflow generating unit 20 further includes an overflow collecting container 28 for collecting the liquid overflowing from the separation container 24. The overflow channel at the upper end of the separation container 24 is connected to the overflow collecting container 28 through a pipeline.

[0047] The nozzle 25 is J-shaped and is placed in the test section of the transparent water tank 10, with its longer vertical section and horizontal section respectively fixed to the side wall and bottom of the transparent water tank 10, and the shorter vertical section fixed to the vertical center plane along the flow direction in the transparent water tank 10. This fixing method can reduce the interference of the nozzle 25 structure on the cross flow velocity.

[0048] By adjusting the height of the separation container 24 , the height difference ∆H between the overflow surface of the separation container 24 and the water level in the transparent water tank 10 is changed, so that the initial rising flow velocity required for the experiment is obtained at the outlet of the nozzle 25 .

[0049] In this embodiment, the liquid storage container 21 and the overflow collection container 28 can be made of white translucent plastic cylinders made of PP material; the peristaltic pump 22 can be a large-flow adjustable-speed peristaltic pump 22, and its maximum flow rate should be greater than the flow rate of the rising flow at the outlet of the nozzle 25 in the experiment to ensure that the separation container 24 can maintain an overflow state in the experiment; the bracket can be an iron stand; the liquid replenishment container 23 can be a cylindrical glass funnel; the separation container 24 can be made of high borosilicate glass, and an overflow channel is set at the upper end, so that the liquid level in the separation container 24 can be maintained at the overflow surface height in the experiment; the upper valve 26 and the lower valve 27 can be made of PP plastic double-pagoda head ball valves, which are respectively used to control the discharge of the liquid replenishment container 23 and the separation container 24; the nozzle 25 can be made of a stainless steel hollow tube, and laser cutting is used to obtain a smooth pipe mouth to minimize the rising flow outlet resistance.

[0050] In one embodiment, the particle release container 30 is used to add particulate matter to the upflow generating unit 20, so that the particulate matter enters the transparent water tank 10 together with the upflow; the particle release container 30 can adopt a glass funnel with a polyfluoro piston to hold the particulate matter required for the experiment. During the experiment, the piston is opened and the particulate matter will enter the rehydration container 23 under the action of gravity, and then enter the transparent water tank 10 from the outlet of the nozzle 25 together with the upflow; the particulate matter can be selected from glass beads, which have good reflectivity and can be illuminated by laser sheet light.

[0051] In one embodiment, the circulating flow generating unit 40 is used to generate a cross flow in the transparent water tank 10; the circulating flow generating unit 40 includes a rectifying component 41, a connecting pipe 42, a water pump 43, a flow meter 44 and a flow generating controller 45, wherein the rectifying component 41 is installed upstream of the transparent water tank 10 to improve the flow quality of the test section of the transparent water tank 10; the transparent water tank 10 can also be divided into a front section, a middle section (test section) and a rear section, wherein the front section and the rear section are the inlet and outlet of the cross flow respectively, and the flow is unstable, and the rectifying component is a honeycomb tube installed between the front section and the middle section of the water tank to stabilize the cross flow and reduce the influence of turbulence on the experiment; the two ends of the connecting pipe 42 are connected to the bottom of the two ends of the transparent water tank 10, the water pump 43 and the flow meter 44 are arranged on the connecting pipe 42, and the water pump 43 and the flow meter 44 are electrically connected to the flow generating controller 45 to realize circulating flow. During the experiment, tap water is injected into the transparent water tank 10 until the experimental water level is reached. The flow rate in the transparent water tank 10 is set by the flow controller 45, and the water pump 43 automatically adjusts the speed to make the flow rate reach the set value, thereby obtaining the cross-flow speed required for the experiment.

[0052] In one embodiment, the shooting unit 50 is used to shoot the motion and diffusion images of particles. The shooting unit 50 includes a computer 51, a synchronizer 52, a laser power supply 53, a laser 54, a light sheet 55 and a high-speed camera. The synchronizer 52 has an input end electrically connected to the computer 51, and an output end electrically connected to the laser power supply 53 and the high-speed camera respectively; the high-speed camera is electrically connected to the computer 51; the laser 54 is connected to the laser power supply 53; the light sheet 55 is installed at the output end of the laser 54; the light sheet 55 is arranged above the outlet of the nozzle 25, the high-speed camera is placed in front of the side wall of the transparent water tank 10, and the lens of the high-speed camera is aimed at the outlet area of ​​the nozzle 25.

[0053] The synchronizer 52 is responsible for controlling the high-speed camera and the laser 54 at the same time, and its input end is electrically connected to the computer 51, and its output end is electrically connected to the high-speed camera and the laser power supply 53; the computer 51 is also electrically connected to the high-speed camera to obtain image information; the sheet light source 55 is arranged at the output end of the laser 54, and the generated laser sheet light passes through the central plane of the transparent water tank 10, which can illuminate the particles on the plane, and at the same time, the high-speed camera takes the image of the particles and uploads it to the computer 51, so as to realize the visualization of the movement of the particles; the laboratory lights need to be turned off during shooting to improve the shooting quality of the particles.

[0054] In the experiment, it is necessary to keep the height difference ∆H between the overflow surface of the separation container 24 and the water level in the transparent water tank 10 unchanged, so as to form an upward flow with a stable initial upward flow velocity at the outlet of the nozzle 25; and by adjusting the height of the separation container 24 to change the height difference ∆H between the overflow surface of the separation container 24 and the water level in the transparent water tank 10, different initial upward flow velocities can be obtained.

[0055] In the experiment, the laser sheet light generated by the sheet light source 55 needs to pass through the central plane of the transparent water tank 10 and illuminate the area near the outlet of the nozzle 25. The purpose is that this area concentrates the main movement and diffusion process of the particles; at the same time, the high-speed camera should be placed directly in front of the side wall of the transparent water tank 10, with the lens aimed at the outlet area of ​​the nozzle 25.

[0056] The embodiment of the present invention further provides a particle transport experimental method based on artificial upwelling, which is implemented in the above-mentioned particle transport experimental device based on artificial upwelling, and includes:

[0057] S1: Add a tracer to the salt water and store them in a liquid storage container 21, and place the particles in a particle release container 30; the temperature and salinity (concentration) of the salt water determine the density of the salt water. The salinity (concentration) of the salt water is calculated according to the density of the upwelling required for the experiment and the water temperature used to prepare the salt water at that time. The concentration of the salt water can be adjusted according to the needs of the experiment. The tracer here can be selected from food pigments;

[0058] S2: According to the initial rising flow velocity required by the experiment, the height of the separation container 24 is adjusted, and the passage between the separation container 24 and the outlet of the nozzle 25 is vented: the upper valve 26 and the lower valve 27 are opened, the peristaltic pump 22 is turned on, and salt water is injected into the separation container 24. When the outlet of the nozzle 25 starts to discharge salt water, the lower valve 27 and the peristaltic pump 22 are closed;

[0059] S3: Inject tap water into the transparent water tank 10 to the experimental water depth. According to the cross-flow speed required by the experiment, set the flow rate in the transparent water tank 10 through the flow controller 45, and the water pump 43 will automatically adjust the speed to make the flow rate reach the set value; turn on the peristaltic pump 22, and continue to inject salt water into the separation container 24 until its water level reaches the overflow surface and maintains the overflow state; open the lower valve 27, at this time, the salt water and tracer in the separation container 24 are discharged from the nozzle 25 and enter the environmental water body in the transparent water tank 10. Since the separation container 24 always maintains the overflow state, a stable upwelling is formed; observe the flow development process of the upwelling through the tracer, and after it is fully developed, open the particle release container 30, at this time, the particles in the particle release container 30 enter the rehydration container 23 under the action of gravity, and then enter the transparent water tank 10 from the outlet of the nozzle 25 together with the upwelling;

[0060] S4: The synchronizer 52 is controlled by the computer 51, and the synchronizer 52 makes the laser power supply 53 and the high-speed camera work synchronously. While the sheet light source 55 generates laser sheet light to illuminate the particles, the high-speed camera takes pictures and uploads the captured movement and diffusion images of the particles to the computer 51.

[0061] Those skilled in the art will readily appreciate other embodiments of the present application after considering the description and practicing the contents disclosed herein. The present application is intended to cover any modification, use or adaptation of the present application, which follows the general principles of the present application and includes common knowledge or customary techniques in the art that are not disclosed in the present application. The description and examples are intended to be exemplary only, and the true scope and spirit of the present application are indicated by the claims.

[0062] It should be understood that the present application is not limited to the precise structures that have been described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof. The scope of the present application is limited only by the appended claims.

Claims

1. A particle transport experimental method based on artificial upwelling, characterized in that: The method is implemented in a particle transport experimental device based on artificial upwelling, and the particle transport experimental device based on artificial upwelling includes: Transparent sink; An upflow generating unit is used to form a stable upflow in the transparent water tank. The upflow generating unit includes a liquid storage container, a peristaltic pump, a liquid replenishment container, a separation container, and a nozzle which are sequentially connected through pipelines. The liquid storage container contains saline and tracer required for the experiment. The peristaltic pump continuously supplies liquid to the liquid replenishment container so that the separation container is in an overflow state during the experiment. The saline and tracer in the separation container are discharged from the nozzle. The height difference ∆H between the overflow surface of the separation container and the water level in the transparent water tank is changed by adjusting the height of the separation container, so as to obtain the initial upflow velocity required for the experiment at the nozzle outlet. The upflow generating unit also includes an upper valve and a lower valve. The upper valve is arranged on the pipeline between the liquid replenishment container and the separation container, and the lower valve is arranged on the pipeline between the separation container and the nozzle. The nozzle is J-shaped, and its longer vertical section and horizontal section are respectively fixed to the side wall and the bottom of the transparent water tank, and the shorter vertical section is fixed to the vertical center plane along the flow direction in the transparent water tank. a particle release container, which adds particles into the rehydration container so that the particles enter the transparent water tank along with the upflow; A circulation flow generating unit, used for generating a cross flow in the transparent water tank; and A shooting unit is used to shoot the movement and diffusion images of particles; the shooting unit includes a computer, a synchronizer, a laser power supply, a laser, a light sheet and a high-speed camera, the synchronizer input end is electrically connected to the computer, and the output end is electrically connected to the laser power supply and the high-speed camera respectively; the high-speed camera is electrically connected to the computer; the laser is connected to the laser power supply; the light sheet is installed at the output end of the laser; the light sheet is arranged above the nozzle outlet, the high-speed camera is placed in front of the side wall of the transparent water tank, and the high-speed camera lens is aimed at the nozzle outlet area; The method includes: S1: Add tracer to saline and store it in a storage container, and place particles in a particle release container; S2: According to the initial rising flow velocity required by the experiment, adjust the height of the separation container and exhaust the channel between the separation container and the nozzle outlet: open the upper valve and the lower valve, start the peristaltic pump, inject salt water into the separation container, wait for the nozzle outlet to start discharging salt water, and then close the lower valve and the peristaltic pump; S3: Inject tap water into the transparent water tank to the experimental water depth. According to the cross-flow speed required by the experiment, set the flow rate in the transparent water tank through the flow controller, and the water pump will automatically adjust the speed to make the flow rate reach the set value; turn on the peristaltic pump and continue to inject salt water into the separation container until its water level reaches the overflow surface and maintains the overflow state; open the lower valve, and the salt water in the separation container is discharged from the nozzle and enters the environmental water body in the transparent water tank. Since the separation container always maintains the overflow state, a stable upwelling is formed; observe the flow development process of the upwelling through the tracer, and after it is fully developed, open the particle release container. At this time, the particles in the particle release container enter the rehydration container under the action of gravity, and then enter the transparent water tank from the nozzle outlet together with the upwelling; S4: The synchronizer is controlled by a computer, which enables the laser power supply and the high-speed camera to work synchronously. While the sheet light source generates laser sheet light to illuminate the particles, the high-speed camera takes pictures and uploads the captured motion and diffusion images of the particles to the computer.

2. The particle transport experimental method based on artificial upwelling according to claim 1, characterized in that: The particle release container, the liquid replenishment container and the separation container are fixed on the bracket from top to bottom by a clamp.

3. The particle transport experimental method based on artificial upwelling according to claim 1, characterized in that: The upflow generating unit further comprises an overflow collecting container for collecting liquid overflowing from the separation container, and the overflow channel at the upper end of the separation container is connected to the overflow collecting container through a pipeline.

4. The particle transport experimental method based on artificial upwelling according to claim 1, characterized in that: The circulating flow-generating unit includes a rectifying component, a connecting pipe, a water pump, a flow meter and a flow-generating controller. The rectifying component is installed upstream of the transparent water tank. The two ends of the connecting pipe are connected to the bottom of the two ends of the transparent water tank. The water pump and the flow meter are arranged on the connecting pipe. The water pump and the flow meter are electrically connected to the flow-generating controller.

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