Hierarchical control structure and method for water diversion tunnels with large fluctuations in water level and flow

Abstract

The present invention relates to a hierarchical control structure and method for a water conveyance tunnel with large water level and flow rate changes, comprising: a vertical shaft with a bottom connected to an upstream pressure tunnel on one side of the upstream, a lower gate provided at the bottom of the downstream side of the vertical shaft, two upper gates provided side by side in the middle, a narrow slit abrupt expansion parabolic reverse arc gentle slope flow channel provided downstream of the lower gate, a parabolic reverse arc steep slope connected to a drop sill flow channel provided downstream of the upper gate, the narrow slit abrupt expansion parabolic reverse arc gentle slope flow channel and the parabolic reverse arc steep slope connected to a drop sill flow channel merge in a downstream stilling pool, and the stilling pool is connected to a downstream pressure-free tunnel. The present invention utilizes a hierarchical control structure to make the water level and flow rate more adaptable, avoids the adverse phenomena such as gate vibration that may be caused by the long-term operation of the gate with a small opening, and both the narrow slit abrupt expansion stilling pool of the lower water intake building and the drop sill bottom flow stilling pool of the upper water intake building have the advantages of no atomization, small bottom plate pulsation pressure, and stable water flow out of the pool, and can ensure safety and reliability.

Description

Technical Field

[0001] The invention relates to a hierarchical control structure and method for a water conveyance tunnel with large water level and flow rate variations, a hydraulic facility and method, and a flow rate control facility and method for a water conveyance tunnel project. Background Art

[0002] Pressurized tunnel water transfer projects usually use radial gates or flat gates to control the water transfer flow. When the water level of the upstream reservoir fluctuates greatly, and the water intake flow also fluctuates greatly to meet the water needs at different stages, in order to ensure that the project can operate safely and reliably under different water level and flow combinations, the requirements for gate control and scheduling are high, and the control is difficult. Especially under high head and small flow conditions, the control gate operates at a small opening for a long time, and the high-speed slit jet of the gate hole is not conducive to the stable operation of the gate, and may even cause safety problems such as gate vibration.

[0003] Controlling water intake in layers according to water level fluctuations is a feasible solution to the problem of small gate openings. However, the structural layout of the stratified water intake buildings in the tunnel, the flow control of the water flow through the gate, and the energy dissipation connection downstream are the key points and difficulties of engineering design. If the design is not reasonable, it is easy to cause engineering safety problems such as cavitation erosion, atomization, turbulent flow, insufficient energy dissipation, drastic fluctuations in the downstream water level, and water flow diversion. Finding a tunnel flow control facility that can adapt to large fluctuations in water level and flow, and is safe and reasonable, is a problem that needs to be solved. Summary of the invention

[0004] In order to overcome the problems of the prior art, the present invention proposes a hierarchical control structure and method for water conveyance tunnels with large water level and flow variations. The structure can ensure good flow through the gate, sufficient energy dissipation, stable water surface, and smooth downstream flow connection in the tunnel, while avoiding the operation of the gate with a small opening, and meet the requirements of safe and reliable operation of the project under different water level and flow combination conditions.

[0005] The object of the present invention is achieved in this way: a hierarchical control structure of a water conveyance tunnel suitable for large changes in water level and flow, comprising: a vertical shaft with a bottom connected to an upstream pressure tunnel on the upstream side, a lower gate is provided at the bottom of the downstream side of the vertical shaft, and two upper gates are provided side by side in the middle, a narrow slit suddenly expanded parabolic reverse arc gentle slope flow channel is provided downstream of the lower gate, and a parabolic reverse arc steep slope and drop-off flow channel is provided downstream of the upper gate, the narrow slit suddenly expanded parabolic reverse arc gentle slope flow channel and the parabolic reverse arc steep slope and drop-off flow channel merge in a downstream stilling pool, and the stilling pool is connected to the downstream pressure-free tunnel.

[0006] Furthermore, a diversion pier is provided between the two upper gates arranged side by side.

[0007] Furthermore, the equation of the anti-arc section curve of the parabolic anti-arc steep slope connecting the drop-off channel is:

[0008]

[0009] In the formula: x1 and y1 are the vertical and horizontal axes of the Cartesian coordinate system of the anti-arc section curve of the parabola anti-arc steep slope connecting the step-down channel; v1 is the average flow velocity of the section at the starting point of the parabola; g is the acceleration of gravity; k is the safety factor used to prevent the generation of negative pressure.

[0010] Furthermore, the drop height d of the parabolic reverse arc steep slope connecting the drop channel is:

[0011] d=(2.5~6.5)h1

[0012] Where: h1 is the thickness of the water tongue at the end of the reverse arc.

[0013] Furthermore, the anti-arc segment curve equation of the narrow slit sudden expansion parabola anti-arc gentle slope flow channel is:

[0014]

[0015] Wherein: x2, y2 are the vertical and horizontal axes of the Cartesian coordinate system of the anti-arc segment curve of the narrow gap sudden expansion parabola anti-arc gentle slope flow channel; v2 is the average flow velocity of the starting section of the parabola.

[0016] Furthermore, the narrow slit upstream contraction ratio λ1 of the narrow slit sudden expansion parabola reverse arc gentle slope flow channel is:

[0017] λ1=b3 / b1=0.4~0.6

[0018] Where: b1 is the upstream width of the narrow slit; b3 is the outlet width of the narrow slit.

[0019] Furthermore, the relative length Δ of the narrow slit of the narrow slit suddenly expanded parabolic reverse arc gentle slope flow channel is:

[0020] Δ=l / b1=1.5~3.0

[0021] Where: l is the shrinkage length.

[0022] Furthermore, the narrow slit downstream diffusion ratio λ2 of the narrow slit sudden expansion parabola reverse arc gentle slope flow channel is:

[0023] λ2=b4 / b3=2.0~5.0.

[0024] Where: b4 is the width of the energy dissipation pool downstream of the narrow gap.

[0025] Furthermore, the parameters of the narrow slot downstream stilling pool of the narrow slot sudden expansion parabola reverse arc gentle slope flow channel include: L j The length of the free water jump; Ls The length of the stilling pool corresponding to the upper water intake structure; L x Length of energy dissipation pool corresponding to the lower water intake structure:

[0026] L j =9.5h1(Fr1-1)

[0027] L s =(0.7~0.8)L j

[0028] L x =(0.4~0.5)L j

[0029] Among them: h1 is the jet water depth under the design flow and water level, for the upper water intake building, it is the end of the reverse arc, and for the lower water intake building, it is the starting contraction section of the narrow gap; Fr1 is the Froude number.

[0030] A layered control method for a water conveyance tunnel with large water level and flow rate variations using the above structure, the method comprising the following steps:

[0031] Step 1, water body stratification: the water body output from the water diversion tunnel is divided into an upper layer and a lower layer;

[0032] Step 2, upper water intake: The upper water intake building adopts a drop-slope bottom flow stilling pool for water flow energy dissipation connection: a mixed flow pattern of submerged jet and submerged water jump is formed in the drop-slope bottom flow stilling pool. With the incident mainstream as a reference, the stilling pool is divided into: submerged jet area, impact area, wall jet area, upper vortex and bottom vortex area:

[0033] The water entering the stilling pool forms a clockwise bottom vortex on the lower side of the mainstream. The mainstream entering the pool quickly sinks to the bottom and then attaches to the bottom under the suction of the bottom vortex. After the mainstream hits the bottom plate of the stilling pool, the flow direction changes, forming a submerged water jump, and a strong counterclockwise vortex is generated on the upper part; in the submerged jet area, the mainstream entering the pool diffuses, mixes, sucks, and turbulently shears along the way, consuming a large amount of kinetic energy and reducing the bottom velocity of the water flow; in the impact area, due to the constraint of the bottom plate of the stilling pool, the flow direction of the water flow changes, and part of the kinetic energy is converted into the pressure energy of the water flow on the bottom plate. The time-averaged and pulsating pressures in the impact area increase sharply, and the mainstream flow velocity decreases rapidly; in the wall-attached jet area, the water flow has obvious submerged water jump characteristics, the bottom mainstream flow velocity decreases along the way, the time-averaged pressure gradually increases, and the pulsating pressure decreases rapidly. Since the mainstream has consumed a large amount of kinetic energy in the impact area, the bottom velocity of the stilling pool bottom plate in the wall-attached jet area is significantly reduced;

[0034] Step 3, water intake from the lower layer: The water intake building at the lower layer adopts narrow gap expansion type energy dissipation pool for water flow energy dissipation connection:

[0035] The high-speed outflow from the control gate generates a rapid shock wave in the narrow slit contraction section, the water depth increases sharply and the Froude number Fr decreases; the high-speed jet aroused by the narrow slit is fully stretched, diffused and aerated vertically, horizontally and longitudinally in the sudden expansion stilling basin, forming a spatial water jump in the stilling basin, and the submerged jet and the spatial water jump intersect and mix with each other in the stilling basin. The water tongue rolls and sucks in air on three sides, the vortex structure is complex, the collision and mixing are intense, the spatial turbulence dissipation is enhanced, the energy dissipation rate is high, and the conjugate water depth and water jump length after the jump are reduced.

[0036] The advantages and beneficial effects of the present invention are as follows: the present invention utilizes a hierarchical control structure to make the water level and flow rate more adaptable, avoids adverse phenomena such as gate vibration that may be caused by long-term operation of the gate at a small opening, and provides flexible gate dispatching and control. The hierarchical control structure of the water diversion tunnel is compactly arranged, has a stable flow pattern, and has good hydraulic performance. Whether it is a narrow gap expansion type energy dissipation pool of the lower water intake building or a drop-sill type bottom flow energy dissipation pool of the upper water intake building, it has the advantages of no atomization, low bottom flow velocity, low bottom plate pulsation pressure, high energy dissipation efficiency, and stable water flow out of the pool, which can ensure the safe and reliable operation of the project. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0038] Figure 1 is a plan view of the structure described in Embodiment 1 of the present invention;

[0039] Figure 2 is a vertical view of the structure described in the first embodiment of the present invention;

[0040] Figure 3 The structure described in the first embodiment of the present invention is Figure 1 AA section view in;

[0041] Figure 4 The structure described in the first embodiment of the present invention is Figure 2 , 3 BB section view in ;

[0042] Figure 5 is a schematic diagram of the structure of the narrow slits described in Embodiments 1, 6, 7, and 8 of the present invention, Figure 1 Enlarged view of point C in the middle;

[0043] Figure 6 Schematic diagram of flow state of upper water intake building of the method described in Embodiment 10 of the present invention;

[0044] Figure 7 It is a schematic diagram of the flow state of the lower water intake building of the method described in Example 10 of the present invention. DETAILED DESCRIPTION

[0045] Embodiment 1:

[0046] This embodiment is a hierarchical control structure suitable for water tunnels with large fluctuations in water level and flow rate, such as Figure 1 , 2 , 3, and 4. The hierarchical control structure described in this embodiment is mainly suitable for water diversion tunnels under conditions where water levels and flow rates often change significantly. The hierarchical control structure mainly includes a pressurized water diversion tunnel, a vertical shaft, an upper water intake building and a lower water intake building, an energy dissipation pool, a downstream pressure-free tunnel, etc. Among them, the upper water intake building includes a control gate, a parabolic reverse arc steep slope section and a drop sill, and a drop sill type bottom flow energy dissipation pool is used for water flow energy dissipation connection; the lower water intake building includes a control gate, a parabolic reverse arc gentle slope section and a narrow gap, and a narrow gap sudden expansion type energy dissipation pool is used for water flow energy dissipation connection.

[0047] The design idea of ​​the structure described in this embodiment is: the upper and lower water intake structures operate independently, the water level control range of the upper and lower gates is determined according to the water level amplitude and flow amplitude, and the water level control range of the upper and lower layers can be non-overlapping or partially overlapping. After adopting layered control, the working head of the upper and lower gates is reduced, avoiding adverse phenomena such as gate vibration that may be caused by the gate opening under high head and small flow conditions.

[0048] This embodiment specifically includes: a vertical shaft 1 whose bottom on the upstream side is connected to the upstream pressure tunnel, a lower gate 2 is provided at the bottom on the downstream side of the vertical shaft, and two upper gates 3 are arranged side by side in the middle, a narrow gap expansion 401 parabolic reverse arc gentle slope 402 flow channel 4 is provided downstream of the lower gate, and a parabolic reverse arc steep slope 501 connecting to a drop-off 502 flow channel is provided downstream of the upper gate, the narrow gap expansion parabolic reverse arc gentle slope flow channel and the parabolic reverse arc steep slope connecting to a drop-off flow channel merge in a downstream stilling pool 6, and the stilling pool is connected to a downstream pressure-free tunnel 7.

[0049] The upper water intake structure is located at a higher position with a large drop in height, and the flow velocity through the gate is relatively high at high water levels. In order to prevent the water from escaping from the bottom of the flow channel and causing cavitation damage, the curve of the falling flow channel is designed to be parabolic to ensure smooth water flow.

[0050] It should be noted that the steep slope and gentle slope are relative to the inclination of the upper and lower chute flow channels, and do not represent the degree of steepness or gentleness.

[0051] The lower water intake structure includes a control gate, a parabolic slope section and a narrow slit. In order to prevent the high-speed water flow behind the gate from escaping from the bottom of the slope and causing cavitation damage, the slope section is designed to be parabolic. The narrow slit includes: an upstream constriction section 403 and a downstream diffusion section 404, such as Figure 5 shown.

[0052] The contraction ratio λ1=b3 / b1 upstream of the narrow gap has a great influence on the flow pattern, water level and velocity distribution in the energy dissipation pool. Generally speaking, the smaller the contraction ratio λ1, the more sufficient the diffusion, aeration and collision of the water flow, and the better the energy dissipation and anti-impact effect downstream; if the contraction ratio λ1 is too small, it may affect the discharge capacity of the gate and form a higher water crown downstream of the narrow gap, affecting the design of the tunnel top elevation. The preliminary design can take the contraction ratio λ1 of the narrow gap as 0.4~0.6 and the relative length l / b1 as (1.5~3.0).

[0053] The diffusion ratio λ2 = b4 / b3 downstream of the narrow gap has a great influence on the flow pattern, energy dissipation efficiency, and engineering excavation volume in the stilling pool. The smaller the diffusion ratio λ2, the smaller the tunnel excavation width, but the conjugate water depth and length required for the stilling pool increase; the larger the diffusion ratio λ2, the larger the tunnel excavation width, and the conjugate water depth and length required for the stilling pool decrease. The preliminary design can take the diffusion ratio λ2 = 2.0 ~ 5.0.

[0054] The length of the stilling pool should be able to ensure that the outflow from the upper and lower water intake structures is fully and evenly diffused. The length of the free water jump, the length of the stilling pool corresponding to the upper water intake structure, the length of the stilling pool corresponding to the lower water intake structure, the design flow rate and the jet depth under the water level, the Froude number and other parameters can be selected by referring to the length of the free water jump.

[0055] Application examples:

[0056] A water transfer project draws water from a reservoir through a pressure tunnel. The gate shaft is used to convert the pressurized water flow into a non-pressurized water flow and then connect it to the downstream non-pressurized tunnel. The normal high water level of the water intake reservoir is 318.48m, the dead water level is 281.48m, and the water level fluctuation is 37.00m. The design flow is 50.0m 3 / s, minimum flow rate 9.4m 3 / s, flow rate range is 40.6m 3 / s. The water level and flow of the water transfer project vary greatly, the gate dispatching and control is difficult, and the flow pattern behind the gate and in the downstream energy dissipation facilities is complex.

[0057] If a single-layer water intake solution is adopted: two arc gates with a width of 2.0m and a height of 3.5m are set at the bottom to control the flow, with a normal high water level of 318.48m and a low flow of 9.4m 3 / s operating condition, when the two gates are opened synchronously, the opening is only 0.105m (relative opening 0.03), the gate opening is too small, the control is difficult, and the high-speed gap jet of the gate hole is not conducive to the long-term safe operation of the gate.

[0058] Adopt double-layer water intake solution:

[0059] 1) A radial gate with a width of 2.0m and a height of 3.5m is set at the lower water intake. The radial gate controls the discharge of a small flow of 9.4m at different water levels. 3The relative opening of / s is 0.079~0.156. Considering that the downstream flow energy of the upper water intake is relatively large under the design water level and flow conditions, in order to reduce the energy dissipation and anti-impact pressure of the downstream energy dissipation pool, the upper water intake is equipped with two arc gates with a width of 1.5m and a height of 3.0m, which reduces the single-width flow of the water flow passing through the gate and increases the flexibility and reliability of scheduling. The single-hole arc gate controls the discharge of a small flow of 9.4m at different water levels. 3 The relative opening of / s is 0.126~0.330.

[0060] 2) The upper water intake building adopts a drop-type bottom flow energy dissipation pool for water flow connection. The flow state in the energy dissipation pool is stable, the energy dissipation is sufficient, and the connection with the downstream pressure-free tunnel water flow is smooth. Compared with the traditional bottom flow energy dissipation pool without a drop, the maximum wave height in the tunnel under the most unfavorable working condition is reduced from 1.019m to 0.670m, and the wave height is reduced by 34%.

[0061] 3) The lower water intake building adopts a narrow gap expansion stilling pool for water flow energy dissipation connection. The flow state in the stilling pool is stable, the energy dissipation is sufficient, and the connection with the downstream pressure-free tunnel water flow is smooth. The maximum wave height in the tunnel under the most unfavorable working condition is reduced from 2.13m in the traditional bottom flow stilling pool and 1.35m in the expansion stilling pool to 0.675m, and the maximum wave height is reduced by 68%.

[0062] Embodiment 2:

[0063] This embodiment is an improvement of the above embodiment and a refinement of the above embodiment regarding the upper gate. A guide pier 301 is provided between the two parallel gates described in this embodiment. Figure 1 .

[0064] The diversion pier is a rectangular structure, with rounded corners on both the water-facing and water-receiving surfaces, forming a regular flow channel with consistent width from front to back.

[0065] Embodiment three:

[0066] This embodiment is an improvement of the above embodiment, and is a refinement of the above embodiment regarding the parabolic reverse arc steep slope connecting the drop-off channel. The reverse arc segment curve equation of the parabolic reverse arc steep slope connecting the drop-off channel described in this embodiment is:

[0067]

[0068] In the formula: x1, y1 are the vertical and horizontal axes of the Cartesian coordinate system of the anti-arc section curve of the parabola anti-arc steep slope connecting the drop-down channel; v1 is the average flow velocity of the parabola starting point section of the parabola anti-arc steep slope connecting the drop-down channel, m / s; g is the acceleration of gravity; k is the safety factor used to prevent the generation of negative pressure, and its value can be selected within the range of 1.2 to 1.6. The larger the safety factor k, the flatter the dam surface curve, the smaller the negative pressure on the dam surface, and the larger the engineering volume; the smaller the safety factor k, the steeper the dam surface curve, the greater the negative pressure on the dam surface, and the smaller the engineering volume.

[0069] Embodiment 4:

[0070] This embodiment is an improvement of the above embodiment, and is a refinement of the above embodiment regarding the drop-off of the parabolic reverse arc steep slope connecting the drop-off channel. The drop-off height d of the parabolic reverse arc steep slope connecting the drop-off channel described in this embodiment is:

[0071] d=(2.5~6.5)h1

[0072] Where: h1 is the thickness of the water tongue at the end of the reverse arc.

[0073] The height of the drop sill directly affects the flow pattern, bottom flow velocity and energy dissipation efficiency in the stilling pool, and should ensure that a submerged bottom flow pattern is formed in the stilling pool. If the drop sill is too low, it is close to the traditional bottom flow pattern, the effect of the drop sill is not obvious, and the bottom flow velocity of the stilling pool is relatively large; if the drop sill is too high, a mixed flow pattern similar to surface flow is formed, and although the bottom flow velocity and the bottom plate pressure pulsation are small, the surface flow velocity and the water surface fluctuation increase, and the energy dissipation rate of the stilling pool is reduced.

[0074] Embodiment five:

[0075] This embodiment is an improvement of the above embodiment, and is a refinement of the above embodiment regarding the narrow slit suddenly expanded parabola reverse arc gentle slope flow channel. The reverse arc segment curve equation of the narrow slit suddenly expanded parabola reverse arc gentle slope flow channel described in this embodiment is:

[0076]

[0077] Wherein: x2, y2 are the vertical and horizontal axes of the Cartesian coordinate system of the anti-arc segment curve of the narrow gap sudden expansion parabola anti-arc gentle slope flow channel; v2 is the average flow velocity of the starting section of the parabola.

[0078] Embodiment six:

[0079] This embodiment is an improvement of the above embodiment, and is a refinement of the above embodiment regarding the narrow slit abrupt expansion parabola reverse arc gentle slope flow channel. The narrow slit upstream contraction ratio λ1 of the narrow slit abrupt expansion parabola reverse arc gentle slope flow channel described in this embodiment is:

[0080] λ1=b3 / b1=0.4~0.6

[0081] Where: b1 is the upstream width of the narrow slit; b3 is the outlet width of the narrow slit, such as Figure 5 shown.

[0082] Embodiment seven:

[0083] This embodiment is an improvement of the above embodiment, and is a refinement of the narrow slit of the above embodiment regarding the narrow slit suddenly expanding parabolic reverse arc gentle slope flow channel. The relative length Δ of the narrow slit suddenly expanding parabolic reverse arc gentle slope flow channel described in this embodiment is:

[0084] Δ=l / b1=1.5~3.0

[0085] Where: l is the shrinkage length, such as Figure 5 shown.

[0086] Embodiment eight:

[0087] This embodiment is an improvement of the above embodiment, which is a refinement of the narrow slit of the narrow slit suddenly expanded parabolic reverse arc gentle slope flow channel in the above embodiment. The narrow slit downstream diffusion ratio λ2 of the narrow slit suddenly expanded parabolic reverse arc gentle slope flow channel described in this embodiment is:

[0088] λ2=b4 / b3=2.0~5.0.

[0089] Where: b4 is the width of the stilling pool downstream of the narrow gap, such as Figure 5 shown.

[0090] Embodiment nine:

[0091] This embodiment is an improvement of the above embodiment, and is a refinement of the parameters of the stilling pool downstream of the narrow slit of the narrow slit suddenly expanded parabolic reverse arc gentle slope flow channel in the above embodiment. The parameters of the stilling pool downstream of the narrow slit of the narrow slit suddenly expanded parabolic reverse arc gentle slope flow channel described in this embodiment include: L j The length of the free water jump; L s The length of the stilling pool corresponding to the upper water intake structure; L x Length of energy dissipation pool corresponding to the lower water intake structure:

[0092] L j =9.5h1(Fr1-1)

[0093] L s =(0.7~0.8)L j

[0094] L x =(0.4~0.5)L j

[0095] Among them: h1 is the jet water depth under the design flow and water level, for the upper water intake building, it is the end of the reverse arc, and for the lower water intake building, it is the starting contraction section of the narrow gap; Fr1 is the Froude number.

[0096] In order to avoid the adverse effects of asymmetric operation of upper and lower water intake structures on the flow state of the energy dissipation pool, such as squeezing the mainstream and deflecting the water flow, a middle partition wall of a certain length can be set in the energy dissipation pool.

[0097] Embodiment ten:

[0098] This embodiment is a hierarchical control method for a water conveyance tunnel with large water level and flow rate variations using the above structure, and the method comprises the following steps:

[0099] Step 1, water stratification: Divide the water output from the water diversion tunnel into upper and lower layers.

[0100] The hierarchical structure used in this embodiment is that the input water body is output from the upper and lower sets of control gates, and the water body is divided into upper and lower layers.

[0101] The following steps 2 and 3 can be performed simultaneously, i.e., water is taken from the upper and lower layers of the water body at the same time, and the opening of the upper and lower layer control gates is used to control the water intake of the upper and lower layers respectively. Steps 2 and 3 can also be performed separately, i.e., water is taken from the lower layer alone, or water is taken from the upper layer alone.

[0102] Step 2, upper water intake: The upper water intake building adopts a drop-slope bottom flow stilling pool for water flow energy dissipation connection. The energy dissipation connection mechanism is: a mixed flow state of submerged jet and submerged water jump is formed in the drop-slope bottom flow stilling pool. With the incident mainstream as a reference, the stilling pool can be divided into: submerged jet area, impact area, wall jet area, upper vortex and bottom vortex area, such as Figure 6 Due to the existence of the drop, the water entering the stilling pool forms a clockwise bottom vortex on the lower side of the mainstream. The mainstream entering the pool quickly sinks to the bottom and then attaches to the bottom under the suction of the bottom vortex. After the mainstream hits the bottom plate of the stilling pool, the flow direction changes, forming a submerged water jump, and a strong counterclockwise vortex is generated on the upper part; in the submerged jet area, the mainstream entering the pool diffuses, mixes, sucks, and turbulently shears along the way, consuming a lot of kinetic energy and reducing the bottom velocity of the water flow; in the impact area, due to the constraint of the bottom plate of the stilling pool, the flow direction of the water flow changes, and part of the kinetic energy is converted into the pressure energy of the water flow on the bottom plate. The time-averaged and pulsating pressures in the impact area increase sharply, and the mainstream flow velocity decreases rapidly; in the wall-attached jet area, the water flow has obvious submerged water jump characteristics, the bottom mainstream flow velocity decreases along the way, the time-averaged pressure gradually increases, and the pulsating pressure decreases rapidly. Since the mainstream has consumed a large amount of kinetic energy in the impact area, the bottom velocity of the stilling pool bottom plate in the wall-attached jet area is significantly reduced. The diffusion, mixing, entrainment and turbulence in the step-down bottom flow stilling pool are strong, the bottom flow velocity is low, the pulsating pressure of the bottom plate is small, the energy dissipation efficiency is high, and the water flow out of the pool is stable.

[0103] Step 3, lower-level water intake: The lower-level water intake structure adopts a narrow-slit sudden expansion energy dissipation pool for water flow energy dissipation connection. The energy dissipation connection mechanism is: the high-speed outflow of the gate generates a rapid shock wave in the narrow-slit contraction section, the water depth increases sharply and the Froude number Fr decreases. The high-speed jet aroused by the narrow slit is fully stretched, diffused and aerated vertically, horizontally and longitudinally in the sudden expansion energy dissipation pool, forming a spatial water jump in the energy dissipation pool. The submerged jet and the spatial water jump intersect and mix with each other in the energy dissipation pool. The water tongue rolls on three sides and sucks in air. The vortex structure is complex, the collision and mixing are intense, the spatial turbulence dissipation is enhanced, the energy dissipation rate is high, and the conjugate water depth and water jump length after the jump are reduced. Figure 7The flow pattern and velocity distribution in the stilling pool have been adjusted and optimized, with low bottom velocity, small pulsating pressure on the bottom plate, small fluctuation of downstream water level, and smooth water flow connection.

[0104] Finally, it should be noted that the above is only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred arrangement scheme, a person skilled in the art should understand that the technical solution of the present invention (such as the structural form of the water transfer project, the application of various formulas, the matching of various hydraulic elements, etc.) can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A hierarchical control structure for a water diversion tunnel with large fluctuations in water level and flow, comprising: A vertical shaft with the bottom of the upstream side connected to the upstream pressure tunnel, a lower gate is provided at the bottom of the downstream side of the vertical shaft, and two upper gates are arranged side by side in the middle, a narrow gap suddenly expanded parabolic reverse arc gentle slope flow channel is provided downstream of the lower gate, and a parabolic reverse arc steep slope and drop-off flow channel is provided downstream of the upper gate, the narrow gap suddenly expanded parabolic reverse arc gentle slope flow channel and the parabolic reverse arc steep slope and drop-off flow channel merge in the downstream stilling pool, and the stilling pool is connected to the downstream non-pressure tunnel; a diversion pier is provided between the two side-by-side upper gates; the anti-arc section curve equation of the parabolic reverse arc steep slope and drop-off flow channel is: In the formula: x1, y1 are the vertical and horizontal axes of the Cartesian coordinate system of the anti-arc segment curve of the parabola anti-arc steep slope connecting the drop-down channel; v1 is the average flow velocity of the starting section of the parabola; g is the acceleration of gravity; k is the safety factor used to prevent the generation of negative pressure; it is characterized in that the drop-down height d of the parabola anti-arc steep slope connecting the drop-down channel is: d=(2.5~6.5)h1 Where: h1 is the thickness of the water tongue at the end of the reverse arc; The curve equation of the reverse arc section of the narrow gap sudden expansion parabola reverse arc gentle slope flow channel is: Where: x2, y2 are the vertical and horizontal axes of the Cartesian coordinate system of the anti-arc segment curve of the narrow gap sudden expansion parabola anti-arc gentle slope flow channel; v2 is the average flow velocity of the starting section of the parabola; The narrow slit upstream contraction ratio λ1 of the narrow slit sudden expansion parabola reverse arc gentle slope flow channel is: λ1=b3 / b1=0.4~0.6 Where: b1 is the upstream width of the narrow slit; b3 is the outlet width of the narrow slit; The relative length Δ of the narrow slit of the narrow slit suddenly expanded parabola reverse arc gentle slope flow channel is: Δ=l / b1=1.5~3.0 Where: l is the shrinkage length; The narrow slit downstream diffusion ratio λ2 of the narrow slit sudden expansion parabola reverse arc gentle slope flow channel is: λ2=b4 / b3=2.0~5.0 Where: b4 is the width of the stilling pool downstream of the narrow gap; The parameters of the narrow slot downstream stilling pool of the narrow slot sudden expansion parabola reverse arc gentle slope flow channel include: j The length of the free water jump; L s The length of the stilling pool corresponding to the upper water intake structure; L x Length of energy dissipation pool corresponding to the lower water intake structure: L j =9.5h1(Fr1-1) L s =(0.7~0.8)L j L x =(0.4~0.5)L j Among them: h1 is the jet water depth under the design flow and water level, for the upper water intake building, it is the end of the reverse arc, and for the lower water intake building, it is the starting contraction section of the narrow gap; Fr1 is the Froude number.

2. A layered control method for a water conveyance tunnel with large water level and flow rate variations using the structure of claim 1, characterized in that: The method comprises the following steps: Step 1, water body stratification: the water body output from the water diversion tunnel is divided into an upper layer and a lower layer; Step 2, upper water intake: The upper water intake building adopts a drop-slope bottom flow stilling pool for water flow energy dissipation connection: a mixed flow pattern of submerged jet and submerged water jump is formed in the drop-slope bottom flow stilling pool. With the incident mainstream as a reference, the stilling pool is divided into: submerged jet area, impact area, wall jet area, upper vortex and bottom vortex area: The water entering the stilling pool forms a clockwise bottom vortex on the lower side of the mainstream. The mainstream entering the pool quickly sinks to the bottom and then attaches to the bottom under the suction of the bottom vortex. After the mainstream hits the bottom plate of the stilling pool, the flow direction changes, forming a submerged water jump, and a strong counterclockwise vortex is generated on the upper part; in the submerged jet area, the mainstream entering the pool diffuses, mixes, sucks, and turbulently shears along the way, consuming a large amount of kinetic energy and reducing the bottom velocity of the water flow; in the impact area, due to the constraint of the bottom plate of the stilling pool, the flow direction of the water flow changes, and part of the kinetic energy is converted into the pressure energy of the water flow on the bottom plate. The time-averaged and pulsating pressures in the impact area increase sharply, and the mainstream flow velocity decreases rapidly; in the wall-attached jet area, the water flow has obvious submerged water jump characteristics, the bottom mainstream flow velocity decreases along the way, the time-averaged pressure gradually increases, and the pulsating pressure decreases rapidly. Since the mainstream has consumed a large amount of kinetic energy in the impact area, the bottom velocity of the stilling pool bottom plate in the wall-attached jet area is significantly reduced; Step 3, water intake from the lower layer: The water intake building at the lower layer adopts narrow gap expansion type energy dissipation pool for water flow energy dissipation connection: The high-speed outflow from the control gate generates a rapid shock wave in the narrow slit contraction section, the water depth increases sharply and the Froude number Fr decreases; the high-speed jet aroused by the narrow slit is fully stretched, diffused and aerated vertically, horizontally and longitudinally in the sudden expansion stilling basin, forming a spatial water jump in the stilling basin, and the submerged jet and the spatial water jump intersect and mix with each other in the stilling basin. The water tongue rolls and sucks in air on three sides, the vortex structure is complex, the collision and mixing are intense, the spatial turbulence dissipation is enhanced, the energy dissipation rate is high, and the conjugate water depth and water jump length after the jump are reduced.

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