A pre-positioned silt-blocking multi-stage herringbone-shaped cycloid weir venturi device

Abstract

The present application belongs to the technical field of low-head fluid kinetic energy recovery and hydroelectric fluid acceleration, in particular to a front blocking silt multi-stage herringbone cambered trochoidal weir Venturi device. The device is provided with a spindle-shaped directional wave concentrating wave pool, a trochoidal flow guide slope surface, a throat pipe, an arc-shaped fence, a streamlined slow-rising slope, a miniature automatic air supplementing device, a garbage cleaning groove, a garbage cleaning frame, a first-stage Venturi acceleration section, a second-stage shallow beach type Venturi acceleration section and a second-stage end contraction nozzle. The device overcomes the defects of the existing vertical steep slope wave making, such as large impact loss, insufficient single-stage Venturi speed increase, inability of a rectangular pool to store directional waves, vortex generated by high-speed jet impact between stages, and fixed stage number unable to adapt to variable hydrological conditions. Meanwhile, the device solves the derivative problems of traditional equipment, such as the inability of waves to be coupled in multiple stages in the same direction, the lack of gradient matching of the size of each stage flow channel, and the induction of cavitation vibration by the overall flow line mutation.

Description

Technical Field

[0001] This invention belongs to the field of low-head fluid kinetic energy recovery and hydropower fluid acceleration technology, specifically a pre-positioned multi-stage herringbone arch cycloidal dike Venturi device. Background Technology

[0002] Low-head water resources are widely distributed in small and medium-sized rivers, water diversion channels, and dams, but their water level difference is small and their water kinetic energy is weak. Conventional water diversion acceleration equipment has extremely low energy utilization rate, and existing equipment has four major defects: First, traditional water intake pools use a vertical steep slope guiding structure. The high-speed impact of water flow on the vertical wall generates a large amount of splashing, vortexes, and backflow. The direction of gravity wave propagation is scattered, and the wave energy is quickly dissipated, making it impossible to achieve the superposition of multiple sets of wave momentum in the same direction. Second, existing fluid acceleration structures are mostly independent single-stage venturis, and there is no integrated series coupling scheme of multi-stage wave pools and multi-stage venturis. Therefore, it is impossible to flexibly increase or decrease the number of acceleration stages according to the water level difference on site, and the kinetic energy improvement is limited under low head conditions. Third, conventional water intake chambers are rectangular pools with equal cross-sections, without dedicated wave-gathering and widening spaces. Waves diffuse and attenuate rapidly along the lateral direction of the pool, and the overall utilization rate of upstream and downstream water level potential energy is less than 30%. Fourth, the existing multi-stage series waterways are all straight-connected sections, with the high-speed jet from the front-stage Venturi directly impacting the inlet of the lower-stage pool, forming a violent impact vortex; at the same time, there is a lack of supporting streamlines for "gradual expansion and stabilization at the end of the Venturi, wave gathering in the middle cavity, and gradual convergence at the tail before entering the lower-stage Venturi", resulting in large head loss between stages and poor wave synergy enhancement effect.

[0003] In summary, to solve the technical problems raised in this paper, this invention proposes a pre-positioned, multi-stage, herringbone arch cycloidal dike Venturi device. Summary of the Invention

[0004] To address the aforementioned shortcomings of existing vertical steep slope wave generation, such as high impact loss, insufficient single-stage Venturi acceleration, inability of rectangular pools to store directional waves, eddy currents generated by high-speed jet impact between stages, and inability to adapt to varying hydrological conditions due to fixed stage numbers; this invention also solves derivative problems such as the inability of traditional equipment to couple waves in the same direction across multiple stages, lack of gradient matching of channel dimensions at each stage, and cavitation vibration induced by abrupt changes in the overall streamline; and provides a pre-positioned, multi-stage, herringbone arch cycloidal dam Venturi device. This device relies on spindle cavity wave focusing, low-loss wave generation via gradient cycloidal flow, progressive acceleration through multiple Venturi stages, and smooth, gradually changing streamlines between stages to eliminate impact. Under a fixed water level difference, it maximizes the kinetic energy of the terminal jet and can be freely configured with two, three, or more stages in series according to the river water level difference.

[0005] To achieve the above objectives, the present invention provides a pre-positioned silt-blocking multi-stage herringbone arch cycloidal dike Venturi device, wherein N stages of kinetic energy enhancement units are sequentially connected in series along the water flow direction, where N≥2; each stage of kinetic energy enhancement unit includes a spindle-shaped directional wave-gathering pool and a matching Venturi acceleration section; the adjacent stages are connected by a continuous streamline layout in which the outlet of the gradually expanding transition section of the preceding stage Venturi connects to the front end of the subsequent stage spindle wave-gathering pool, and the gradually contracting confluence port at the tail end of the spindle wave-gathering pool connects to the contraction inlet of the current stage Venturi.

[0006] The directional wave-gathering wave pool is a spindle-shaped cavity with narrow cross-sections at both ends and the widest cross-section in the middle along the water flow axis. The inlet area at the front end of the directional wave-gathering wave pool has a gradually narrowing structure, the confluence area at the tail end gradually narrows the confluence opening, and the widened area in the middle is used to accumulate directional shallow water gravity waves generated by the cycloidal slope. Each stage of the directional wave-gathering wave pool is equipped with a cycloidal guide slope with the steepest descent line in the widened area in the middle. The outlet end of each stage of the cycloidal guide slope is smoothly tangent to the contraction inlet of the Venturi acceleration section of the same stage. The curve equation of the steepest descent line (cycloid) is x=r(t-sint), y=r(1-cost), where the parameter t takes values ​​in the range of 0≤t≤π. This section of the curve is the semi-arch section of the cycloid, and its arch height H=2r.

[0007] The Venturi acceleration section is sequentially configured with a contraction inlet, a contraction nozzle, and a gradually expanding transition section at the end along the water flow; the final stage of the Venturi acceleration section of the entire device is equipped with a final jet outlet at the tail end for outputting high-speed water flow.

[0008] The complete two-stage layout structure of the entire device is as follows: An upstream pressure-stabilizing water storage area is set up, and the outlet of the upstream pressure-stabilizing water storage area is connected to the first-stage spindle-shaped directional wave-forming pool through an arc-shaped fence and a streamlined gentle slope; The first-stage spindle-shaped directional wave-forming pool is equipped with a cycloidal guide slope, and the bottom of the cycloidal guide slope is smoothly connected to the contraction inlet of the first-stage Venturi acceleration section; a gradually expanding transition section is set at the tail of the first-stage Venturi acceleration section. The outlet of the first-stage Venturi gradual expansion transition section smoothly connects to the front end of the second-stage spindle-shaped directional wave-forming pool. A cycloidal guide slope is arranged in the middle of the second-stage spindle-shaped directional wave-forming pool. The tail end of the second-stage spindle-shaped directional wave-forming pool gradually narrows to connect to the contraction inlet of the second-stage shallow shoal-type Venturi acceleration section. A terminal contraction nozzle is set at the end of the second-stage Venturi acceleration section, and the nozzle outlet connects to the downstream low-water-level outlet area.

[0009] When the water level difference in the river channel is greater, the third, fourth and even Nth kinetic energy enhancement units can be connected in series after the second-stage kinetic energy enhancement unit; all expansion units uniformly adopt the unified structural form of "spindle-shaped directional wave-forming pool + gradient cycloidal guide slope + differentiated venturi acceleration section + interstage gradual expansion + gradually contracting smooth streamline".

[0010] The overall structure of this invention is uniformly defined by the following features: 1. The cycloidal guide slopes inside the spindle-shaped directional wave-gathering pools at all levels are all standard steepest descent curves with no right angles or vertical abrupt changes in cross-section, and the water flows down without impact throughout the entire process; 2. The cross-sectional dimensions of each stage of the Venturi acceleration section are differentiated along the water flow. The upstream unit adopts a deep and narrow pipe channel, the final unit adopts a flat, wide and shallow channel, and the middle channel smoothly transitions from deep to shallow. The height-to-width ratio of the flat channel is less than 0.2. 3. Along the direction of water flow, the arch height and base circle radius of the cycloidal guide slope of the previous stage are both greater than those of the cycloidal guide slope of the next stage, forming a gradient wave energy distribution that matches the wave amplitude that decays at each stage. 4. All cycloidal guide slopes, the inner wall of the spindle-shaped directional wave-forming pool, and the Venturi acceleration section are smooth tangential curved surfaces at the connection points, without any local sudden expansion or contraction sections, thus suppressing the generation of eddies and cavitation. 5. Adjacent kinetic energy enhancement units are continuously connected, and the front-stage Venturi gradually expanding outlet is seamlessly tangentially connected to the front end of the lower-stage spindle-shaped directional wave-forming pool. 6. Each stage of the spindle-shaped directional wave-concentrating wave pool is a spindle-shaped cavity, narrow at both ends of the axis, with the widest cross-sectional width in the middle, a gradually narrowing front end, and a gradually narrowing confluence port at the rear end. 7. A complete and gradually changing streamline channel is formed between stages: the end of the Venturi acceleration section of the previous stage gradually expands → the front end of the spindle-shaped directional wave-forming pool gradually narrows → the middle wave-forming and widening zone of the spindle-shaped directional wave-forming pool → the tail end of the spindle-shaped directional wave-forming pool gradually narrows and merges → the contraction entrance of the next stage Venturi acceleration section. The entire process is smooth and there is no high-speed jet impact on the cross section. 8. The diffusion angle α of the gradually expanding transition section at the end of the previous stage Venturi acceleration section is ≤8° to ensure that the boundary layer does not separate within the gradually expanding section and to eliminate the backflow vortex region.

[0011] Furthermore, at least the last stage of the cycloidal guide slope is designed as a modular and detachable structure, and the cycloidal curvature and slope installation height can be adjusted on-site according to the inflow rate and the difference between upstream and downstream water levels; the number of series units of the entire device can be freely selected according to hydrological conditions.

[0012] Furthermore, along the water flow direction, the maximum cross-sectional width of the middle section of each stage of the spindle-shaped directional wave-gathering pool is greater than the width of its front inlet and tail confluence cross-section; the maximum width of the middle section of the previous stage of the spindle-shaped directional wave-gathering pool is greater than the maximum width of the middle section of the next stage of the spindle-shaped directional wave-gathering pool, which matches and adapts to the progressively decreasing cycloidal size and wave amplitude.

[0013] This invention has two major significant technical advantages over existing technologies: 1. Multi-level gradient cycloid + differentiated Venturi-based synergistic advantages: 1.1 Cycloidal flow with ultra-low loss: The water flows smoothly down the standard steepest descent line without impact or splashing; the head loss of the single-stage wave generation section is reduced by 18%~26% compared with the traditional vertical steep slope, generating gravity waves that propagate in a directional manner without lateral scattering energy loss. 1.2 Multi-stage wave momentum synergistic superposition: Each stage independently generates shallow water gravity waves in the same direction, and the waves are continuously coupled and superimposed in the subsequent cavity and Venturi; the flow velocity at the end of the two-stage structure is more than 25% higher than that of the traditional single-stage straight slope equipment, and the efficiency improvement of three-stage and above series devices continues to increase; the entire process is driven only by the potential energy of natural water level, without external pressurization equipment such as water pumps. 1.3 Gradient Differentiated Venturi Matching Flow Field: The upstream deep and narrow Venturi completes the initial kinetic energy boost, the downstream flat and shallow shoal Venturi adapts to shallow waves, and the middle channel smoothly transitions, making full use of the dynamic pressure fluctuations brought by wave undulations. 1.4 Flexible adaptation to various working conditions: The energy units can be increased or decreased according to the water level difference of the channel or dam, adapting to multiple scenarios such as small channels with small drops and power stations in rivers with large drops; 1.5 Low cost of civil engineering renovation: The existing water diversion channel wall can be directly used for renovation, without the need to add large water-retaining structures. 1.6 High equipment operational stability: The fully smooth streamlined structure significantly reduces the probability of cavitation, vibration, and siltation failures, extending service life.

[0014] 2. The spindle-shaped wave-concentrating cavity and the interstage gradually expanding and contracting streamlines offer exclusive efficiency advantages. 2.1 Spindle cavity wave focusing and energy focusing: The widened space in the middle of the spindle pool stably accommodates regular gravity waves, restricts the lateral diffusion of waves, prolongs the duration of wave momentum coupling, and the multi-stage superposition of kinetic energy is additionally increased by 10%~15%; 2.2 Completely eliminate interstage impact loss: After the high-speed water flows out of the Venturi throat, it gradually decreases in velocity and stabilizes in the terminal expansion section before flowing into the front end of the spindle pool; the gradually narrowing confluence at the tail end of the spindle pool evenly gathers the undulating water and sends it into the next stage Venturi, further reducing the interstage turbulent head loss by about 12%; 2.3 Natural constraint on wave propagation direction: The narrowing curved surface of the spindle inhibits lateral backflow of water, and waves of all levels always propagate in the same direction, greatly widening the flow rate adaptation range; 2.4 Fully Continuous Streamline Noise and Vibration Reduction: The cycloidal surface, spindle inner wall, and Venturi gradient section are all tangentially integrated, with no high-pressure abrupt changes in the cross-section, further reducing equipment operating noise, vibration, and cavitation risks.

[0015] 3. The combined advantages of curved fences and trash collection boxes; 3.1 The arc-shaped fence filters the water flow entering the spindle-shaped directional wave-forming pool, preventing impurities such as fallen leaves and dead wood from the external water source from entering the spindle-shaped directional wave-forming pool; thus preventing blockage at the tail end of the spindle-shaped directional wave-forming pool. 3.2 When external water enters the spindle-shaped directional wave-gathering pool, it passes through an arc-shaped fence. The arc-shaped transition surface of the fence guides the garbage, causing it to collect in the garbage collection box, thus facilitating garbage collection and cleaning. 3.3 The bottom of the garbage collection box is slidably connected to the garbage collection trough via pulleys. When garbage enters the garbage collection box, the garbage collection box can be pulled left and right to remove it from the garbage collection trough for unified cleaning of the garbage inside.

[0016] Energy conservation statement: This invention requires no external energy input throughout the entire process; the kinetic energy of the outlet jet originates entirely from the potential energy of the water body corresponding to the water level difference between the upstream and downstream sides. Each flow channel within the device experiences a head loss greater than zero, ensuring that the total kinetic energy at the outlet is always less than the initial potential energy increment, strictly adhering to Bernoulli's equation and the law of conservation of energy. The "efficiency enhancement" described in this invention refers only to increasing the percentage of potential energy converted into kinetic energy through optimizing the flow surface and reducing turbulence and impact losses. Attached Figure Description

[0017] Figure 1 This is a structural view of the secondary kinetic energy enhancement unit in this invention; Figure 2 yes Figure 1 Top view in the middle; Figure 3 This is an internal structural view of the kinetic energy enhancement unit in this invention; Figure 4 This is a structural view of the Chinese-language acceleration section and the terminal contraction nozzle of the present invention; In the diagram: 1. Spindle-shaped directional wave-forming pool; 2. Cycloidal guide slope; 3. Throat; 4. Arc-shaped fence; 5. Streamlined gentle slope; 6. Miniature automatic air replenishment device; 11. Garbage collection trough; 12. Garbage collection frame; 7. First-stage Venturi acceleration section; 8. Second-stage shallow-shoal type Venturi acceleration section; 9. Second-stage end contraction nozzle.

[0018] Description of the attached diagram: Water flows out from the upstream high-water-level stabilizing water storage area, passes through the streamlined gently rising slope 5 and the arc-shaped fence 4, and enters the first-stage spindle-shaped directional wave-forming pool 1; the first-stage spindle-shaped directional wave-forming pool 1 is narrow at the front, has the largest cross-sectional width in the middle, and smoothly narrows at the tail; the water body smoothly slides down the previous stage cycloidal guide slope 2 to generate the first set of directional gravity waves, and accumulates in the widened space in the middle of the spindle-shaped directional wave-forming pool 1; the undulating water flow enters the first-stage Venturi acceleration section 7, is accelerated through the throat 3 of the first-stage contraction nozzle, and then smoothly diffuses through the terminal gradually expanding transition section to eliminate the high-speed concentrated jet; After diffusion, the water flow smoothly enters the front end of the secondary spindle-shaped directional wave-forming pool 1, which gradually narrows. The second set of co-directional gravity waves is generated on the cycloidal guide slope 2 of the second stage in the pool. The two sets of waves complete momentum coupling and superposition in the middle of the secondary spindle pool. The coupled water is sent to the secondary shallow venturi acceleration section 8 through the gradually narrowing confluence port at the tail of the secondary spindle-shaped directional wave-forming pool 1. After being accelerated twice by the secondary end contraction nozzle 9, it is discharged into the downstream low-water-level outlet area.

[0019] The attached diagram only shows a two-stage series structure. The three-stage and above extended units all adopt the same spindle wave-gathering, gradient cycloid, and interstage gradually changing streamline structure, and will not be drawn again in the attached diagram. Detailed Implementation

[0020] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0021] Example 1: Two-stage small-scale prototype The overall longitudinal length of the machine is 10m, with a fixed upstream and downstream water level difference of 1.5m; the structural dimensions are as follows: Upstream pressure-stabilizing water storage area: 2.2m in length, 0.9m in steady-state water depth; The first-stage spindle-shaped directional wave-gathering pool 1 has a total axial length of 2.4m, a front inlet section width of 0.45m, a maximum section width of 1.1m in the middle, and a tail confluence section width of 0.5m; the first-stage cycloidal guide slope 2 has an arch height of 0.6m, a cycloidal base circle radius of 0.5m, and the water outlet end of the slope is smoothly tangent to the first-stage Venturi. First-stage Venturi acceleration section 7: inlet cross-sectional width 0.8m, first-stage contraction nozzle cross-sectional width 0.25m, contraction ratio 3.2:1; end-stage gradual diffusion transition section length 1.6m, diffusion angle α=5.6°; Secondary spindle-shaped directional wave-gathering pool 1: axial total length 1.8m, front inlet section width 0.4m, middle maximum section width 0.95m, tail confluence section width 0.42m; secondary cycloidal guide slope 2 arch height 0.35m, cycloidal base circle radius 0.4m; Second-stage shallow venturi acceleration section 8: flat channel height 0.18m, second-stage terminal contraction nozzle 9 cross-section width 0.3m; The steady-state water depth in the downstream low-water-level outflow area is 0.4m.

[0022] Prototype test operation data: The control group used a traditional vertical steep slope and a rectangular water diversion device with a uniform cross-section, at Q=0.35m. 3 Under the conditions of the same upstream water level (1.5m), the same rated flow rate, and the same final stage outlet cross-sectional area as the final stage nozzle area in this embodiment, the measured terminal flow velocity is 2.48m / s. The flow velocity at the end of the rectangular wave pool and the non-spindle wave-gathering structure is 3.12 m / s. The complete solution of the present invention, which combines spindle concentrating wave and interstage gradual expansion and contraction, has an end flow velocity of 3.47 m / s. All the comparative experiments were conducted under the same inflow rate and outlet back pressure conditions to ensure that the velocity increase was solely due to the optimization of the internal flow channel structure of the device. Compared with traditional equipment, the overall velocity increase was 39.9%, while the combined head loss from wave generation and interstages was only 5% to 8%.

[0023] Example 2: Industrialized equipment for low-head waterways in third-level rivers Applicable scenarios: Small and medium-sized river low-head power stations, with a design water level drop of 4.5m and a channel rated flow of 800m³. 3 / h, a three-stage series kinetic energy enhancement unit; First-level unit parameters: Spindle-shaped directional wave-gathering pool 1 inlet width 0.52m, maximum width in the middle 1.25m, tail confluence width 0.55m; cycloidal arch height 0.7m, base circle radius 0.55m; first-level Venturi shrinkage ratio 3.5:1; Secondary unit parameters: Spindle-shaped directional wave-gathering pool 1 has an inlet width of 0.44m, a maximum width in the middle of 1.08m, and a tail confluence width of 0.46m; cycloidal arch height of 0.45m and base circle radius of 0.42m; secondary Venturi shrinkage ratio of 2.8:1; Parameters of the third-level unit: the inlet width of the spindle-shaped directional wave-forming pool 1 is 0.36m, the maximum width in the middle is 0.88m, and the confluence width at the tail is 0.38m; the cycloidal arch height is 0.25m, and the base circle radius is 0.30m; the height-to-width ratio of the final stage flat Venturi channel is less than 0.15.

[0024] t∈[0,π],H=2r. All cycloidal slopes are processed as semi-arched cycloids. The tangent at the end of the slope and the tangent point at the Venturi inlet is horizontal, ensuring that the water flows in smoothly with zero angle of attack.

[0025] Supporting optimized structure: The cycloidal slopes at all levels are lined with wear-resistant integral concrete, and the slopes are formed by casting precast steel templates. The curved surface of the templates is processed by CNC machine tools according to the parametric equations x=r(t-sint), y=r(1-cost), (t∈[0,π]); the throat pipes 3 at all levels are lined with anti-corrosion and wear-resistant coatings; micro automatic air replenishment devices 6 are added to the first and second level units to suppress cavitation, and the air replenishment devices are existing air valves; the bottom of the third-level spindle-shaped directional wave-gathering pool 1 is equipped with guide ribs to enhance the shallow water gravity wave-gathering focusing effect.

[0026] Field test results: Compared with traditional straight slope water diversion channels, the inlet kinetic energy of the turbine of the two-stage series device is increased by 23%, and the overall kinetic energy of the three-stage series device is increased by 46%. The engineering selection rule is to add one kinetic energy unit for every 1.2~1.5m increase in water level difference. The number of stages can be flexibly adjusted according to the river hydrological data. This embodiment does not constitute a limitation on the upper limit of the number of stages of the device.

[0027] Complete workflow of the device (applicable to both levels, and the same applies to multiple levels) Water at a constant level first flows into the upstream pressure-stabilized water storage area to stabilize the water flow and eliminate impurities. The stable water then passes through the arc-shaped fence 4 and the streamlined gentle slope 5. The arc-shaped fence 4 blocks impurities in the water. Driven by the water, the impurities in the water enter the garbage collection box 12. The filtered water then enters the first-stage spindle-shaped directional wave-generating pool 1. The spindle cavity, which is narrow at the front and wide in the middle, constrains the direction of the water flow. The water slides smoothly down the first-stage cycloidal guide slope 2 without impact, generating continuous and stable directional shallow water gravity waves, which accumulate in the widened area in the middle of the spindle pool. Water carrying stable waves flows into the first-stage Venturi acceleration section 7, is initially accelerated through the throat 3, and then gradually decelerates through the terminal gradual diffusion transition section to eliminate high-speed concentrated jets. Since the diffusion angle α≤8° of this gradual diffusion section, the water flow adheres well to the boundary layer during diffusion and no separation vortex is generated. Therefore, it can enter the lower-stage spindle-shaped directional wave-forming pool 1 with a uniform low turbulence flow state. After diffusion, the smooth, undulating water flow smoothly merges into the front end of the secondary spindle-shaped directional wave-forming pool 1, which gradually narrows. The water body generates a second set of unidirectional gravity waves along the secondary cycloidal guide slope 2. The two sets of waves are fully coupled and superimposed in the middle space of the secondary spindle-shaped directional wave-forming pool 1. The coupled water body is evenly gathered at the tail end of the secondary spindle-shaped directional wave-forming pool 1 and sent into the secondary flat shallow shoal venturi acceleration section 8 to complete the secondary acceleration; finally, the high-speed water flow is ejected from the secondary end contraction nozzle 9, impacting the turbine to do work or completing the high-pressure channel water transport, and then flows into the downstream low-water-level outlet area.

[0028] If three, four or more stages are configured, each stage repeats the cycle of "pre-stage Venturi gradual expansion and stabilization flow → spindle-shaped directional wave-forming pool 1 middle wave-forming coupling → tail-end gradual contraction and converging flow into the next stage Venturi", amplifying the kinetic energy of the end water outlet stage by stage.

[0029] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A pre-positioned, multi-stage, herringbone-shaped cycloidal dike Venturi device, characterized in that, N stages of kinetic energy enhancement units are connected in series along the water flow direction, where N≥2; Each stage of the kinetic energy enhancement unit includes a spindle-shaped directional wave-forming pool (1) and a Venturi acceleration section connected to the tail of the spindle-shaped directional wave-forming pool (1). The spindle-shaped directional wave-forming pool (1) described in the previous stage includes a spindle-shaped inner cavity, which has a front inlet area, a middle widening area and a tail confluence area along the water flow axis; the front inlet area has a narrow cross section, the middle widening area has a wide cross section and the tail confluence area has a narrow cross section; there is a cycloidal guide slope (2) between the front inlet area and the middle widening area, and there is an acceleration throat (3) in the tail confluence area; The front entrance area of ​​the first-stage spindle-shaped directional wave-forming pool (1) is covered with an arc-shaped fence (4), and the front end of the arc-shaped fence (4) is provided with a streamlined gentle slope (5). Between the two adjacent kinetic energy enhancement units, the end of the acceleration throat (3) of the previous stage is provided with a gradually expanding transition section. The outlet of the gradually expanding transition section and the spindle-shaped directional wave-forming pool (1) of the next stage have a cycloidal guide slope (2). The outlet of the gradually expanding transition section and the cycloidal guide slope (2) are tangential curved surfaces that are seamlessly connected. The middle part of the spindle-shaped directional wave-forming pool (1) of the next stage is a widening structure. A continuous gradually changing streamline channel is formed, consisting of "gradually expanding transition section → widening in the middle of the spindle pool → gradually narrowing confluence at the tail". Along the water flow direction, the cross-sectional dimensions of the Venturi acceleration sections at each stage decrease progressively. The upstream unit is a deep and narrow channel, the final unit is a flat, wide, and shallow channel, and the channels at each intermediate stage smoothly transition from deep and narrow to flat, wide, and shallow. The aspect ratio of the flat, wide, and shallow channel at the final stage is less than 0.

2.

2. The Venturi device for a pre-positioned, multi-stage, herringbone arch cycloidal dike according to claim 1, characterized in that: The diffusion angle α of the gradually expanding transition section at the end of the previous stage Venturi acceleration section is ≤8°, and the inner wall of the gradually expanding transition section is a smooth curved surface.

3. The Venturi device for a pre-positioned, multi-stage, herringbone arch cycloidal dike according to claim 1, characterized in that: The top of the arc-shaped fence (4) is reserved with a garbage cleaning trough (11) at the inlet of the previous spindle-shaped directional wave pool (1). A garbage cleaning frame (12) is set inside the garbage cleaning trough (11). The garbage cleaning frame (12) is slidably connected to the bottom of the garbage cleaning trough (11) by bottom pulleys.

4. The Venturi device for a pre-positioned, multi-stage, herringbone arch cycloidal dike according to claim 1, characterized in that: Along the direction of water flow, the base circle radius and arch height of the cycloidal guide slope (2) of the later stage are 0.6 to 0.85 times that of the base circle radius and arch height of the cycloidal guide slope (2) of the previous stage, respectively; along the direction of water flow, the maximum cross-sectional width of the middle section of the spindle-shaped directional wave-forming pool (1) of the previous stage is greater than the maximum cross-sectional width of the middle section of the spindle-shaped directional wave-forming pool (1) of the later stage.

5. The Venturi device for a pre-positioned, multi-stage, herringbone arch cycloidal dike according to claim 4, characterized in that: At least the last stage of the cycloidal guide slope (2) is a modular disassembly structure, and its cycloidal curvature and installation height can be adjusted on-site according to the inflow rate and the difference between upstream and downstream water levels.

6. The Venturi device for a pre-positioned, multi-stage, herringbone arch cycloidal dike according to claim 4, characterized in that: All the cycloidal guide slopes (2) described at each level are precast steel templates cast into a structure. The curved surface of the precast steel template is based on the brachistochrone equation x=r(t-sint) and y=r(1-cost), where 0≤t≤π, and is processed by CNC machine tools.

7. The Venturi device for a pre-positioned, multi-stage, herringbone arch cycloidal dike according to claim 4, characterized in that: Except for the final stage, each of the Venturi acceleration stages is equipped with a miniature automatic air supply device (6) in the throat (3) to suppress negative pressure cavitation in the throat.

8. The Venturi device for a pre-positioned, multi-stage, herringbone arch cycloidal dike according to claim 1, characterized in that: The bottom of the inner cavity of the spindle-shaped directional wave pool (1) of the final stage is provided with guide ribs extending along the water flow direction to enhance the focusing effect of shallow water gravity wave pooling.

9. The Venturi device for a pre-positioned, multi-stage, herringbone arch cycloidal dike according to claim 1, characterized in that: The number of series stages of the N-stage kinetic energy enhancement unit is freely selected according to the river water level difference, with an additional stage added for every 1.2~1.5m increase in water level difference.

10. A low-head hydroelectric power generation system, characterized in that, The device includes a pre-emergence silt-blocking multi-stage herringbone arch cycloidal dike Venturi device as described in any one of claims 1 to 9, wherein the outlet of the final stage Venturi acceleration section of the device is arranged facing the inlet of the turbine, for directly impacting the turbine with the accelerated jet to perform work.

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