Low water head after-sluice underflow combined energy dissipater adaptive to large tidal range of tidal estuary

Abstract

The low water head post-sluice underflow combined energy dissipater comprises a post-sluice stilling pool, a plurality of triangular piers are evenly arranged at the position, n meters away from the horizontal distance of a slope bottom, of a slope section of the front section of the post-sluice stilling pool at intervals, n = (Hpool-1.3 Htriangular pier) * k, Hpool is the designed pool depth of the post-sluice stilling pool, k is the designed pool depth of the post-sluice stilling pool, and k is the designed pool depth of the post-sluice stilling pool. H is the height of the triangular pier, and k is the gradient of the slope section; the vertical face, parallel to the water flow direction, of the triangular pier is triangular, the section, perpendicular to the water flow direction, of the triangular pier is rectangular, and the top of the triangular pier is provided with a lifting corner upwards lifted towards the middle side of the stilling pool behind the gate. The top elevation of the triangular pier is slightly lower than the top elevation of the tail sill, and the elevation difference between the top elevation of the triangular pier and the top elevation of the tail sill is 0.3 H of the triangular pier. Under various hydraulic conditions, especially under the downstream low water level condition, the energy dissipation and scour prevention effects are remarkable, and the device can well adapt to the large tidal range condition with large downstream water depth fluctuation.

Description

Technical Field

[0001] The utility model relates to the technical field of bottom flow energy dissipation behind a low-head dam gate, in particular to a combined bottom flow energy dissipation device behind a low-head dam gate adapted to large tidal differences in tidal estuaries. Background Art

[0002] Traditional low-head dams typically utilize underflow energy dissipation pools as the energy dissipation structure behind the sluice gates. A single stilling pool, relying solely on the water cushion within the pool, is ineffective, requires a long pool length and depth, and results in significant project investment. Therefore, a stilling pool combined with auxiliary energy dissipation structures is often used to reduce its length and depth.

[0003] The journal article "A Review of Common Auxiliary Energy Dissipators for Sluice Underflow Energy Dissipation" (Guo Zhining, Jilin Water Conservancy, Issue 01, pp. 51-56, January 2024) discloses that common auxiliary energy dissipators for sluice underflow include force dissipation piers, wide tail piers, tail sills, and suspended screens. Common force dissipation pier types include rectangular piers, trapezoidal piers, toe piers, and T-shaped piers. Based on their placement, they can be divided into front piers, middle piers, and rear piers.

[0004] The stilling piers located in the center of the stilling basin typically include stilling piers and stilling beams. These piers and beams, due to their strong reaction force from the rapids, provide a high level of auxiliary energy dissipation, promoting the formation of a forced hydraulic jump and significantly shortening the stilling basin. However, in practical engineering, stilling piers and beams are susceptible to cavitation damage from high-speed water flow, as well as impact and abrasion damage from entrained sand and gravel. Consequently, their practical application has drawbacks and limitations.

[0005] The toe pier is located at the end or toe of the front section of the stilling basin. Its primary function is to disperse the high-speed rapids entering the stilling basin into multiple streams, thereby reducing the Froude number and the second conjugate depth of the hydraulic jump, thereby reducing the basin depth and length. However, due to the toe pier's uniform shape and placement, it generally does not significantly improve the stilling basin's energy dissipation rate.

[0006] When a single auxiliary energy dissipation facility is used in a stilling pool and cannot meet the energy dissipation requirements, in order to improve the energy dissipation rate, multiple auxiliary energy dissipators can be combined together, and different auxiliary energy dissipators can be used to produce different water flow characteristics, thereby improving the energy dissipation efficiency.

[0007] In the combined energy dissipation of the tail sill, USBR-Ⅳ type stilling pool (for specific layout, see Figure 1 A USBR-IV energy dissipator is a combined toe pier and continuous tailwater sill, suitable for Froude numbers between 2.5 and 4.5. Compared to traditional stilling basins, this type does not shorten the basin length, but effectively dissipates surface waves. USBR-IV stilling basins require a 5%-10% submergence to address the tailwater sensitivity of the hydraulic jump at low Froude numbers.

[0008] Large weirs located at the mouth of a tidal river are subject to high discharge volumes, large tidal ranges in the downstream water level, and frequent tidal fluctuations. When the gates are fully opened to discharge floodwater, the impact of energy dissipation and anti-scouring measures is minimal due to the higher downstream water level. However, when the initial openings are low, or a few openings are high, the large tidal range in the tidal river causes significant fluctuations in the water depth behind the gates. When the downstream water level is low, a long-range hydraulic jump is easily formed in the stilling basin behind the gates. The residual energy of the water flow behind the tail sill is still significant, which can easily scour and damage anti-scouring facilities such as the floodplain behind the stilling basin, thereby endangering the safe discharge of the weir. The USBR-IV stilling basin is less adaptable to large tidal ranges with large fluctuations in downstream water depth. Utility Model Content

[0009] In order to solve the above problems, the purpose of the utility model is to provide a low-head lock-behind bottom flow combined energy dissipator that can adapt to the large tidal range in tidal estuaries. It has significant energy dissipation and anti-scouring effects under various hydraulic conditions, especially under low water level conditions downstream, and can better adapt to large tidal range conditions with large fluctuations in downstream water depth.

[0010] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0011] A low-head bottom flow combined energy dissipation device adapted to large tidal ranges in tidal estuaries comprises a stilling pool behind the gate, wherein a plurality of triangular piers are evenly spaced at a position n meters horizontally away from the bottom of the slope section in front of the stilling pool behind the gate, wherein the vertical surface of the triangular pier parallel to the water flow direction is triangular, and the cross section of the triangular pier perpendicular to the water flow direction is rectangular, and the top of the triangular pier is provided with a cantilever angle upwardly projecting toward the middle part of the stilling pool behind the gate; the top elevation of the triangular pier is slightly lower than the top elevation of the tail sill of the rear section of the stilling pool behind the gate, and the elevation difference between the top elevation of the triangular pier and the top elevation of the tail sill is 0.3H 三角墩 ; where n=(H 池 -1.3H 三角墩 )×k,H 池 H is the design depth of the stilling pool behind the gate, 三角墩 is the height of the triangular pier, k is the slope of the slope section; the height of the triangular pier H 三角墩 It is 1.07h1, where h1 is the water depth of the contraction section.

[0012] As a specific implementation method, the energy dissipation pool behind the gate includes a pool body formed by a slope section, a horizontal bottom plate section and a tail sill arranged in sequence, and side guide walls arranged on both sides of the pool body; the slope section is arranged at an angle, the upper end of the slope section is connected to the bottom plate of the gate chamber of the dam, the lower end of the slope section is connected to one end of the horizontal bottom plate section arranged horizontally close to the dam, and the other end of the horizontal bottom plate section is connected to the tail sill.

[0013] As a specific implementation, the tail sill is vertically arranged close to the side wall of the sluice.

[0014] As a specific implementation manner, the angle α of the pick angle is 1°≤α≤5°.

[0015] As a specific implementation, the angle α of the pick is 5°.

[0016] As a specific implementation manner, the slope k of the slope section is 3≤k≤4.

[0017] As a specific implementation manner, the slope k of the slope section is 3.

[0018] As a specific implementation manner, the width b of the triangular pier is equal to the water depth h1 of the contraction section; the distance s between the triangular piers is b≤s≤1.3b, and b is the width of the triangular pier.

[0019] As a specific implementation, the distance s between the triangular piers is 1.25b, where b is the width of the triangular pier.

[0020] The utility model has the following beneficial effects:

[0021] This low-head, post-sluice, combined energy dissipation device, designed to adapt to large tidal ranges in tidal estuaries, allows the water flow through the gate to differentially flow into the pool, forcing a hydraulic jump to occur earlier and controlling its location, transforming a remote-driven hydraulic jump into a submerged one. This stabilizes the downstream flow pattern, contributing to riverbed and bank stability and ecological environmental protection. The device fully utilizes the water cushion depth in the stilling basin, improving the energy dissipation rate, making it less sensitive to changes in downstream water depth and more adaptable to large tidal ranges in tidal river sections. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a structural diagram of the USBR-Ⅳ type stilling basin;

[0023] Figure 2 This is a schematic diagram of the top view of the structure of the utility model;

[0024] Figure 3 This is a schematic diagram of the main structure of the utility model;

[0025] Figure 4 This is an enlarged structural diagram of the triangular pier of the present utility model;

[0026] Figure 5 Schematic diagram comparing the energy dissipation effects of four structures (including the present utility model);

[0027] Figure 6 This is a schematic diagram of the energy dissipation effect of a stilling pool without triangular piers;

[0028] Figure 7 This is a schematic diagram of the energy dissipation effect of the combined energy dissipation structure where the elevation of the triangular pier top is higher than the elevation of the tail sill top;

[0029] Figure 8 The elevation of the triangular pier top is lower than the elevation of the tail sill top and the elevation difference is greater than 0.3H 三角墩 Schematic diagram of energy dissipation effect of combined energy dissipation structure;

[0030] Figure 9 It is a schematic diagram of the energy dissipation effect of the energy dissipation and anti-impact structure of the present invention. DETAILED DESCRIPTION

[0031] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0032] See also Figures 2 to 4 A low-head bottom flow combined energy dissipation device behind the gate adapted to the large tidal range in a tidal estuary includes a stilling pool 10 behind the gate. The stilling pool 10 behind the gate includes a pool body formed by a slope section 11, a bottom plate section 12 and a tail sill 13 arranged in sequence, and side guide walls 14 arranged on both sides of the pool body. The slope section 11 is arranged obliquely, and the upper end of the slope section 11 is connected to the bottom plate of the gate chamber of the dam, and the lower end of the slope section 11 is connected to one end of the horizontally arranged bottom plate section 12 close to the dam, and the other end of the bottom plate section 12 is connected to the vertically arranged tail sill 13. Specifically, the tail sill 13 is vertically arranged close to the side wall of the dam.

[0033] A plurality of triangular piers 20 are evenly spaced at a horizontal distance n meters from the bottom of the slope section 11. The vertical surface of the triangular pier 20 parallel to the direction of water flow is a triangle, and the cross section of the triangular pier 20 perpendicular to the direction of water flow is a rectangle. The top of the triangular pier 20 is provided with a cantilever angle that is raised toward the middle side of the energy dissipation pool 10 behind the gate (i.e., the side of the bottom plate section 12). The cantilever angle, i.e., the angle α between the top surface of the triangular pier 20 and the horizontal plane, is 1°≤α≤5°, preferably 5°. The top elevation of the triangular pier 20 is slightly lower than the top elevation of the tail sill 13, and the elevation difference between the top elevation of the triangular pier 20 and the top elevation of the tail sill 13 is 0.3H. 三角墩 .

[0034] Where n=(H 池 -1.3H 三角墩 )×k,H 池 H is the design depth of the stilling pool behind the gate, 三角墩 is the height of the triangular pier, k is the slope of the slope section, where the slope k = l / h, l is the horizontal distance of the slope surface, and h is the vertical height of the slope surface. The slope k of the slope section 11 is 3≤k≤4, preferably 3. The height H of the triangular pier 20 三角墩 It is 1.07h1, where h1 is the water depth of the contraction section.

[0035] The width b of the triangular pier 20 is equal to the water depth h1 of the contraction section, that is, b=h1; the distance s between the triangular piers 20 is b≤s≤1.3b, where b is the width of the triangular pier.

[0036] The slope section 11 of the stilling pool 10 behind the gate guides the overflow in the gate chamber into the stilling pool 10 behind the gate. Part of the flow enters through the cantilevered injection at the top of the triangular pier 20, and part of the flow enters through the contracted channel between the triangular piers 20. The two differential water flows enter the stilling pool 10 behind the gate in layers. The thickness of the jet in the direction perpendicular to the water depth increases exponentially, and the water flow is fully diffused in the cross section to become a whole. The water flow after diffusion at the top is continuously aerated, fragmented, and mixed in the air, resulting in an increase in the cross-sectional area of ​​the water flow, prompting a hydraulic jump to occur at the tail of the triangular pier 20. The fully aerated water flow is injected into the stilling pool 10 behind the gate as additional momentum for hydraulic jump energy dissipation, forming multiple small-scale three-dimensional vortices in the stilling pool 10 behind the gate. Through the effect of the three-dimensional hydraulic jump that mixes with each other, the corresponding second conjugate water depth is reduced, and the original remote-driven hydraulic jump in the stilling pool 10 behind the gate is transformed into a submerged hydraulic jump, reducing the pressure of downstream energy dissipation and anti-impact, achieving the purpose of controlling the location of the hydraulic jump and improving the energy dissipation rate of the stilling pool. The horizontal design of the bottom of the bottom plate section 12 causes the water flow in the pool to roll and diffuse to reduce kinetic energy. A vertical tail sill 13 is set at the tail of the stilling pool to maintain a certain water cushion in the stilling pool for inflow energy dissipation.

[0037] In a specific embodiment, the total length of the post-sluice stilling pool 10 is 47.00m, of which the slope section 11 is 10.50m long, the remaining post-sluice stilling pool 10 after the slope section 11 is 36.50m long, and the post-sluice stilling pool 10 is 2.00m deep. The slope section 11 has a slope of 3. The triangular pier 20 serves as an auxiliary energy dissipator. The top angle of the triangular pier 20 is a 5° cantilever angle. The width of the triangular pier 20 is 1.20m, the height is 1.28m, and the horizontal length of the triangular pier 20 is 3.00m. The triangular pier 20 is set at a position where the slope section 11 of the post-sluice stilling pool 10 is 1.00m horizontally away from the bottom of the slope. The distance between the triangular piers 20 is 1.50m.

[0038] By setting up a comparative scheme (stilling basin + triangular pier with no angled bend + tail sill), and by controlling the height of the downstream water level, the comparative verification verified that the present scheme (stilling basin + triangular pier with 5° angled bend + tail sill) can achieve excellent energy dissipation effects under various hydraulic conditions. The triangular pier 20 of the present scheme is set at a 5° angle and is located at a horizontal distance of 1.00m from the bottom of the slope section 11 of the stilling basin 10 behind the gate. The top elevation of the triangular pier 20 is slightly lower than the top elevation of the tail sill 13, with an elevation difference of 0.38m. The top surface of the triangular pier 20 of the comparative scheme is flat and is located at the bottom of the slope section 11 of the stilling basin 10 behind the gate. The top elevation of the triangular pier 20 is 1.20m lower than the top elevation of the tail sill 13. The other parameters of the comparative scheme are the same as those of the present scheme.

[0039] Under the same working condition of gate opening e=3.00m,

[0040] When the downstream water level is 4.79m, a high submerged flow forms in the stilling pool 10 behind the gate of this scheme, and its submerged surface flow can reach near the end of the gate chamber. The water level in the stilling pool 10 behind the gate is slightly lower than the downstream water level. The flow velocity distribution of the 30th section of the floodplain behind the tail sill is relatively uniform, and the flow velocity continuously decreases along the way. The maximum bottom flow velocity is greatly reduced, with an average flow velocity of 2.04m / s. The average flow velocity of the comparative scheme is 2.65m / s.

[0041] When the downstream water level is lowered to 0.11m, the rapids on the slope section 11 behind the gate of this scheme diffuse and collide with the triangular pier 20 with a cantilever to form a multi-component mixed flow with no obvious hydraulic jump. A tumbling water flow is formed in the stilling basin to dissipate considerable kinetic energy. The flow velocity of the apron section 30 is 3.15m / s, while the flow velocity of the apron section 30 of the comparative scheme is 6.09m / s.

[0042] From the above data comparison, it can be seen that the triangular pier 20 of the comparison scheme cannot adapt to changes in downstream water levels. As the water level changes, the flow velocity varies greatly, which can easily cause scouring or washing of the downstream sea flood protection section 30. However, this scheme is more adaptable to large tidal ranges and extremely unfavorable low tides in the tidal river estuary. Under various hydraulic conditions, especially under low water level conditions downstream, the energy dissipation and anti-scouring effects have obvious advantages over the original traditional combined energy dissipation device.

[0043] Through experimental research, it was found that under extremely unfavorable hydraulic conditions of a 4.68m drop in the downstream water level, the maximum flow velocity attenuation rate in the middle section of the apron 30 behind the 10-step stilling pool behind the sluice gate reached 48%, and the kinetic energy attenuation rate in the key section reached 73%.

[0044] Under the extremely unfavorable condition of a water level difference of 4.86m, the proposed scheme exhibited a relatively small variation of 54% in flow velocity between high and low water levels in section 30 of the floodplain. The variation under the comparative scheme was 129% under both conditions. This demonstrates that the proposed scheme's low-head post-sluice bottom flow combined energy dissipation device, designed to accommodate large tidal ranges in tidal estuaries, is well-suited to large tidal ranges and extremely unfavorable low tides in tidal estuary sections.

[0045] The location of the hydraulic jump in a flat-bottomed stilling basin is significantly affected by changes in the tailwater level. By setting a slope in front of the triangular pier of the stilling basin, the hydraulic jump can be controlled near the inflection point. Because the sluice gate is located in a tidal river section, the water level downstream of the gate is affected by the tide and fluctuates greatly and frequently. When the downstream tidal level is lower than the elevation of the stilling basin's tailwater sill, the stilling basin can only rely on the 2m water cushion in the pool to dissipate energy. At this time, the location and height of the triangular pier 20 are particularly important. By allowing the hydraulic jump to occur earlier, the length of the stilling basin can be shortened, improving the downstream energy dissipation situation.

[0046] Through experiments and comparative analysis, we concluded that:

[0047] In the first case, when the triangular pier 20 is not set, the water jump tail position is moved to about 7.00m downstream of the slope inflection point. Figure 5 and Figure 6 .

[0048] In the second case, the triangular pier 20 is set too high. When the top of the triangular pier 20 is higher than the water depth of the stilling pool, part of the water flowing down the outflow slope of the sluice gate will form a jet from the top of the triangular pier 20 and enter the pool, causing turbulence on the water surface. In addition, the water jump does not occur near the triangular pier 20, but near the slope inflection point. The jump tail is about 4.50m away from the slope inflection point. For details, see Figure 5 and Figure 7 ;

[0049] In the third case, the position of triangular pier 20 is too low, and the water jump basically occurs near the slope inflection point, and the jump tail is about 4.50m away from the slope inflection point. Figure 5 and Figure 8 ;

[0050] In the fourth case, i.e., this solution, the triangular pier 20 is positioned on a slope so that the pier top elevation is near the tail sill elevation. In this case, the water flowing down the slope increases the thickness of the jet in the direction perpendicular to the chute, and the water flow is fully diffused in the cross section to form a whole. The effect of the water cushion in the stilling basin is fully utilized, forming a stable water jump near the triangular pier 20 with a good shape. The head of the water jump is located upstream of the slope inflection point, and the tail of the jump is located about 2.00m downstream of the inflection point. For details, see Figure 5 and Figure 9 .

[0051] In summary, the triangular pier 20 with a cantilevered angle can transform the remote-driven water jump in the stilling pool into a submerged water jump. The triangular pier 20 is arranged on the slope section 11 so that the top elevation of the triangular pier 20 is basically the same as the top elevation of the tail sill of the stilling pool. The water cushion in the stilling pool can be fully utilized for energy dissipation, the water jump is stable, and the water jump occurs earlier, which can shorten the length of the stilling pool. It is not dependent on changes in the downstream tidal level and can further adapt to changes in the downstream water depth.

[0052] The above is only a specific implementation method of the present invention, and does not limit the patent scope of the present invention. Any equivalent structural transformation made using the contents of the description and drawings of the present invention, or directly or indirectly applied in other related technical fields, is also included in the patent protection scope of the present invention.

Claims

1. A low-head lock-back bottom flow combined energy dissipator adapted to large tidal ranges in tidal estuaries, characterized by: The invention comprises a stilling pool (10) behind the gate, wherein a plurality of triangular piers (20) are evenly spaced at a position at a horizontal distance n meters from the bottom of the slope section (11) in the front section of the stilling pool (10) behind the gate, wherein the vertical surface of the triangular pier (20) parallel to the water flow direction is triangular, and the cross section of the triangular pier (20) perpendicular to the water flow direction is rectangular. The top of the triangular pier (20) is provided with a cantilever angle which is cantilevered toward the middle side of the stilling pool (10) behind the gate; the top elevation of the triangular pier (20) is slightly lower than the top elevation of the tail sill (13) at the rear section of the stilling pool (10) behind the gate, and the elevation difference between the top elevation of the triangular pier (20) and the top elevation of the tail sill (13) is 0.3H. 三角墩 ; Where n=(H 池 -1.3H 三角墩 )×k,H 池 H is the design depth of the stilling pool behind the gate, 三角墩 is the height of the triangular pier, k is the slope of the slope section, and the height H of the triangular pier (20) 三角墩 It is 1.07h1, where h1 is the water depth of the contraction section.

2. The low-head lock-back bottom flow combined energy dissipator adapted to large tidal ranges in tidal estuaries according to claim 1 is characterized by: The energy dissipation pool (10) behind the gate comprises a pool body formed by a slope section (11), a horizontal bottom plate section (12) and a tail sill (13) arranged in sequence, and side guide walls (14) arranged on both sides of the pool body; the slope section (11) is arranged obliquely, the upper end of the slope section (11) is connected to the bottom plate of the gate chamber of the river sluice, the lower end of the slope section (11) is connected to one end of the horizontal bottom plate section (12) arranged horizontally close to the river sluice, and the other end of the horizontal bottom plate section (12) is connected to the tail sill (13).

3. The low-head lock-back bottom flow combined energy dissipator adapted to large tidal ranges in tidal estuaries according to claim 2 is characterized by: The tail sill (13) is vertically arranged close to the side wall of the dam.

4. The low-head lock-back bottom flow combined energy dissipator adapted to large tidal ranges in tidal estuaries according to claim 1 is characterized by: The angle α of the pick angle is 1°≤α≤5°.

5. The low-head lock-back bottom flow combined energy dissipator adapted to large tidal ranges in tidal estuaries according to claim 1 or 4, characterized in that: The angle α of the pick is 5°.

6. The low-head lock-back bottom flow combined energy dissipator adapted to large tidal ranges in tidal estuaries according to claim 1 is characterized by: The slope k of the slope section (11) is 3≤k≤4.

7. The low-head lock-back bottom flow combined energy dissipator adapted to large tidal ranges in tidal estuaries according to claim 1 or 6, characterized in that: The slope k of the slope section (11) is 3.

8. The low-head lock-back bottom flow combined energy dissipator adapted to large tidal ranges in tidal estuaries according to claim 1 is characterized by: The width b of the triangular pier (20) is equal to the water depth h1 of the contraction section; the distance s between the triangular piers (20) is b≤s≤1.3b, where b is the width of the triangular pier.

9. The low-head lock-back bottom flow combined energy dissipator adapted to large tidal ranges in tidal estuaries according to claim 8 is characterized by: The distance s between the triangular piers (20) is 1.25b, where b is the width of the triangular pier.

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