A diversion tunnel outlet shaft energy dissipation structure

Abstract

The present invention relates to an energy dissipation structure for a diversion tunnel outlet shaft, comprising a shaft, an inlet section, and a diversion tunnel. The shaft is provided with a bottom plate at its bottom, and the bottom of the shaft is a closed structure. An inlet and an overflow are provided on the shaft wall of the shaft. One end of the inlet section is connected to the inlet, and the other end of the inlet section is connected to the diversion tunnel. The centerline of the inlet in the width direction is eccentric to the vertical axis of the shaft, and the bottom elevation of the overflow is between the elevation of the inlet section bottom plate and the elevation of the inlet section top plate. The present invention has a simple structure and is easy to construct. It can fully eliminate the kinetic energy of the water flowing down the diversion tunnel, and can reduce the single-width flow rate of the water flowing down, disperse the excess energy, and guide the water flow to the middle of the downstream river channel, thereby reducing the load on the bank slope and the bank flow velocity.

Description

Technical Field

[0001] The present invention relates to the technical field of flood discharge and energy dissipation in water conservancy and hydropower projects, and in particular to an energy dissipation structure for a vertical shaft at a diversion tunnel outlet. Background Art

[0002] As a new type of energy dissipator, the vertical shaft swirl energy dissipator has been widely used in the design of flood discharge and energy dissipation in spillway tunnels of water conservancy and hydropower projects in recent years. It has the advantages of flexible layout, outflow direction not restricted by the upstream tunnel section, high energy dissipation rate, etc. It can adapt to complex terrain and geological conditions such as narrow river valleys and high drop heights. It is usually arranged in combination with diversion tunnels, which greatly saves project investment. The vertical shaft of the vertical shaft swirl spillway tunnel is arranged in the mountain on the inlet side, such as Figure 1 As shown, it mainly includes: an upper flat section 13, an exhaust pipe 8, a vortex chamber 9, a contraction section 10, a vertical shaft section 11, and a lower flat section 12. The incoming flow enters the vertical shaft through the upper flat section, and the water flows downward along the shaft wall. The air cavity in the center of the shaft serves as the air inlet channel, allowing the water to be fully aerated. The water then enters the stilling well at the bottom to dissipate energy, and finally enters the lower flat section through the pressure outlet. Its fundamental characteristics are three: first, the inflow into the vertical shaft is open flow; second, the water flows along the wall, with the air cavity at the center of the shaft being a continuous flow, which belongs to the category of water-air two-phase flow; third, the stilling well at the bottom is used to dissipate energy, and the water enters the lower flat section through the pressure outlet.

[0003] Large diversion tunnels in water conservancy and hydropower projects generally have long tunnel lines and large flow rates. Due to the project's topographical and geological conditions and project investment restrictions, the outflow direction of the diversion tunnel often intersects the river channel at a large angle, which puts great pressure on the energy dissipation and anti-scouring of the downstream river channel. This problem is particularly prominent when large diversion tunnels are arranged in narrow river valleys. Generally, there are no energy dissipation facilities at the diversion tunnel outlet, and the energy dissipation mainly relies on the water body of the downstream river channel. When the angle between the outflow direction and the river channel is large, the effective energy dissipation water length of the downstream river channel will be significantly reduced, and the energy dissipation will be insufficient. The outflow from the diversion tunnel crosses the river channel to reach the opposite bank, resulting in a higher flow velocity on the opposite bank and a larger dynamic water load on the bank slope. According to conventional design, concrete cast-in-place anti-scouring piles and concrete panels are generally used for protection. Due to the deep pile foundation, cofferdam construction may even be required, and the protection range is large, so the project investment is also large. However, the vortex shaft in the existing technology is not suitable for dissipating the energy of the water flow at the diversion tunnel outlet. Summary of the Invention

[0004] The purpose of the present invention is to address the deficiencies of the prior art and provide a diversion tunnel outlet vertical shaft energy dissipation structure to solve the problem of water energy dissipation at the diversion tunnel outlet.

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

[0006] A diversion tunnel outlet shaft energy dissipation structure comprises a shaft, an inlet section, and a diversion tunnel. A bottom plate is provided at the bottom of the shaft, and the bottom of the shaft is a closed structure. An inlet and an overflow are provided on the wall of the shaft. One end of the inlet section is connected to the inlet, and the other end of the inlet section is connected to the diversion tunnel. The center line of the inlet in the width direction is eccentric to the vertical axis of the shaft, and the elevation of the bottom of the overflow is between the elevation of the inlet section bottom plate and the elevation of the inlet section top plate.

[0007] The flow from the diversion tunnel enters the vertical shaft through the inlet section. The water flows obliquely downward and in a rotating manner along the wall of the vertical shaft, and continues to rotate and flow upward after reaching the bottom of the vertical shaft. The bottom elevation of the overflow port is between the elevation of the bottom plate of the inlet section and the elevation of the top plate of the inlet section. The bottom of the vertical shaft is a closed structure, so that a certain amount of water remains in the center of the vertical shaft. The water in the center of the vertical shaft is dragged by the main flow attached to the wall, forming an obvious vortex flow state. In this process, due to the significant increase in the flow rate of the water flow, the frictional resistance is enhanced. In addition, the strong shear and rotational flow formed by the main flow attached to the wall and the water in the center of the vertical shaft causes the turbulence intensity of the water flow to increase significantly, so that the downstream water flow can fully dissipate energy in the vertical shaft. The water body that has undergone energy dissipation overflows into the downstream river channel through the overflow port to avoid scouring the river channel.

[0008] Furthermore, the horizontal cross-section of the vertical shaft is circular, and the inlet section is tangent to the vertical shaft.

[0009] Optionally, the cross-section of the inlet section is the same as or different from the cross-section of the diversion hole.

[0010] Furthermore, the inlet section is a section of the diversion tunnel close to the vertical shaft.

[0011] Optionally, the length of the inlet section is no less than five times the height of the diversion tunnel. This provides a buffering effect, facilitating water flow adjustment and flow pattern control, and preventing drastic changes in water flow from the diversion tunnel to the inlet. A folded slope forms between the bottom slope of the inlet section and the bottom slope of the diversion tunnel. If the inlet section is too short, the local load within the diversion tunnel will increase significantly, and the cross-sectional flow velocity distribution will vary significantly, preventing the water flow from reaching a relatively uniform state before entering the shaft.

[0012] Optionally, the length of the inlet section is more than 10 times the width of the diversion hole.

[0013] Furthermore, the floor of the inlet section has a slope ranging from 5% to 15%, with the elevation of the floor gradually decreasing along the outflow direction. Preferably, the slope is 10%. This ensures that after the water enters the shaft and swirls, it does not impact the top of the shaft.

[0014] Furthermore, the overflow port is an annular opening arranged on the shaft wall toward the river channel.

[0015] Alternatively, the overflow opening's central angle and direction can be determined based on the downstream river's topographical conditions. This adjusts the outflow direction from the diversion tunnel and reduces erosion of the riverbank. The vertical shaft should maintain a free surface even at the diversion tunnel's maximum flow rate, preventing pressurized flow from affecting discharge capacity.

[0016] Preferably, the central angle of the annular opening ranges from 90° to 180°.

[0017] Furthermore, the top elevation of the overflow port is higher than the free water surface elevation in the shaft when the diversion tunnel discharges the maximum flow.

[0018] After selecting the overflow opening's central angle, estimate the required weir crest head using practical weir flow calculation formulas, taking into account downstream water level connection conditions. The overflow's top elevation should be higher than the free water surface elevation within the shaft when the diversion tunnel discharges maximum flow. When the diversion tunnel discharge is low, the overflow exhibits free weir flow or a drop flow pattern. When the discharge is high, the overflow exhibits a submerged weir flow pattern. A wider overflow disperses the flow energy, reducing downstream protection pressure.

[0019] Furthermore, the radius of the horizontal cross-section of the shaft is 1.5-2 times the width of the inlet section. The internal space of the shaft is a regular cylinder. The greater the design flow rate of the diversion tunnel, the larger the radius of the horizontal cross-section of the shaft. When the shaft radius is smaller than the above value, the curvature of the shaft wall is large, which is not conducive to the swirling flow of the incoming flow in the shaft, and will cause a greater impact on the shaft wall; when the shaft radius is larger than the above value, the energy dissipation effect can be increased and the swirling flow state can be improved, but the corresponding engineering workload will increase. In addition, the layout will be limited by the influence of topographic and geological conditions.

[0020] Furthermore, the height of the vertical shaft is greater than that of the inlet section, the bottom plate of the vertical shaft is lower than the bottom plate of the inlet section, and the top plate of the vertical shaft is higher than the top plate of the inlet section. This ensures that water flows into the vertical shaft from the middle, allowing the water to swirl downward and upward to dissipate energy, thereby improving energy dissipation efficiency.

[0021] Furthermore, measured from the top of the inlet section, the height of the vertical shaft is greater than 1 times the height of the inlet section.

[0022] Furthermore, the depth of the shaft is 1-2 times the height of the inlet section, thus ensuring sufficient swirl space in the shaft.

[0023] Optionally, the top of the shaft is an open structure or an underground cavern structure.

[0024] Furthermore, a bottom plate is provided at the bottom of the shaft. A certain amount of water is retained at the bottom of the shaft, so that the water at the bottom of the shaft can dissipate energy from the incoming flow. There is no through-hole air cavity in the center of the shaft, and the water flow is a complete vertical axis tumbling flow. The water overflows through the overflow port above the shaft, which can maintain a good flow state and a low flow rate.

[0025] Furthermore, a free water surface should always be maintained in the shaft. Once flooding occurs, the discharge capacity of the diversion tunnel will be reduced.

[0026] Optionally, a drainage channel is provided between the overflow port and the river channel, wherein the drainage channel is a drainage channel having a width comparable to that of the overflow port.

[0027] Furthermore, the inlet section is provided with a top plate. When the discharge flow from the diversion tunnel is small, there is a free water surface in the inlet section, and the inlet section is open flow. When the diversion tunnel discharges a large amount of flood water, there is no free water surface in the inlet section, and the inlet section is pressurized flow.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) The inlet flow of the shaft structure of the present invention can be open flow or pressurized flow. The water flow rotates along the wall and dissipates energy through friction and shearing the water body in the center of the shaft. There is no through air cavity in the center of the shaft. It is a complete vertical axis rotating water flow. The water overflows through the overflow port above the shaft instead of being a pressurized outflow, which fully dissipates the energy of the water flow.

[0030] (2) The present invention has a simple structure and can fully eliminate the kinetic energy of the water flowing down the diversion tunnel, and can reduce the single-width flow rate of the water flowing down, disperse the excess energy, and guide the water flow to the middle of the downstream river channel, thereby reducing the load on the bank slope and the bank flow velocity.

[0031] (3) The present invention has strong applicability and is particularly suitable for designing diversion tunnels with long distances, large flow rates, and large intersection angles between the outflow direction and the river channel in narrow river valleys. It can fundamentally solve the problem of energy dissipation and anti-scouring in the river channel near the diversion tunnel outlet.

[0032] (4) The present invention is easy to construct and can be constructed together with the diversion tunnel, eliminating the need for special construction to protect the downstream river channel near the diversion tunnel outlet, thereby saving project investment. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic diagram of the shaft structure in the prior art;

[0034] Figure 2 It is a schematic diagram of the planar structure of the present invention;

[0035] Figure 3 It is a schematic diagram of the cross-sectional structure of the present invention;

[0036] Figure 4 It is a horizontal cross-sectional velocity contour diagram of a comparative example of the present invention;

[0037] Figure 5 It is the horizontal cross-sectional velocity vector diagram of the comparative example of the present invention;

[0038] Figure 6 is a horizontal cross-sectional velocity contour map of an embodiment of the present invention;

[0039] Figure 7 1 is a horizontal cross-sectional flow velocity vector diagram of an embodiment of the present invention.

[0040] Explanation of the accompanying symbols: 1. diversion tunnel; 2. inlet section; 3. vertical shaft; 4. overflow; 5. spillway; 6. river channel; 7. inlet; 8. exhaust pipe; 9. vortex chamber; 10. contraction section; 11. vertical shaft section; 12. lower flat section; 13. upper flat section; the direction of the arrow indicates the direction of water flow; θ is the central angle of the overflow. DETAILED DESCRIPTION

[0041] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments. It should be noted that the embodiments and features of the embodiments may be combined unless they conflict. For ease of description, the words "upper," "lower," "left," and "right" appear below merely to indicate the directions of upper, lower, left, and right in the accompanying drawings and do not limit the structure.

[0042] Example

[0043] See Figure 2 and Figure 3 A diversion tunnel outlet shaft energy dissipation structure includes a shaft 3 and an inlet section 2. The bottom of the shaft 3 is provided with a bottom plate, and the bottom of the shaft 3 is a closed structure. An inlet 7 and an overflow port 4 are provided on the wall of the shaft 3. One end of the inlet section 2 is connected with the inlet port 7, and the other end of the inlet section 2 is connected with the diversion tunnel 1. The center line of the inlet port 7 in the width direction is eccentric to the vertical axis line of the shaft 3. The bottom elevation of the overflow port 4 is between the elevation of the bottom plate of the inlet section 2 and the elevation of the top plate of the inlet section 2.

[0044] The inlet section 2 passes through the vertical shaft 3, and one side wall of the inlet section 2 is tangent to the wall of the vertical shaft 3. Figure 2 As shown in the figure, along the water flow direction, the right side wall of the inlet section is tangent to the right side wall of the shaft, and a counterclockwise vortex is generated in the shaft. When the left side wall of the inlet section is tangent to the left side wall of the shaft, a clockwise vortex is generated in the shaft.

[0045] The inlet floor elevation of diversion tunnel 1 of a large hydropower station project is 2015m, the outlet floor elevation is 2013m, the total length is approximately 1550m, and the bottom slope is 0.13%. Diversion tunnel 1 is a gate tunnel section with cross-sectional dimensions of 17m×19m, a top arch central angle of 120°, and a cross-sectional area of ​​298.74㎡. The maximum design flow rate of diversion tunnel 1 is approximately 6700m 3 / s, the average flow velocity of the corresponding section is 22.4m / s, the intersection angle between the outlet section axis and the river channel 6 is about 53°, the width of the outlet section is about 90m-130m, and the thickness of the riverbed cover is about 30m (the lower limit elevation of the strongly weathered bedrock is about 1983m).

[0046] The diversion tunnel 1 has a gate-like cross-section, measuring 17m x 19m (width x height), a top arch central angle of 120°, a cross-sectional area of ​​298.74 square meters, a bottom slope of 0.13%, and an angle of intersection with the river channel of 53°. The inlet section 2 has the same cross-section as the diversion tunnel 1, is 200m long, and has a bottom slope of 10%. The inlet section 2 intersects with the vertical shaft 3, and the right side wall of the inlet section 2 is tangent to the right side wall of the vertical shaft 3, forming a spatially curved inlet 7 on the wall of the vertical shaft 3. The top elevation of this curved surface is 2018m, and the bottom elevation is 1999m.

[0047] The cross-sectional radius of the vertical shaft 3 is 34m, which is twice the width of the diversion tunnel 1. The elevation of the bottom plate of the vertical shaft 3 is 1983m, and the elevation of the top of the vertical shaft 3 is 2050m (located in the mountain). The elevation difference between the bottom plate of the vertical shaft 3 and the bottom plate at the end of the inlet section 2 is 15m, which is about 1 times the height of the diversion tunnel 1. The elevation difference between the top of the vertical shaft 3 and the top of the inlet section 2 is 32m.

[0048] The opening center angle θ of the overflow port 4 is 180°, and the opening width is 106.8m (overflow front length). If the terrain conditions of the downstream river channel 6 allow, the opening center angle is preferably 180°, so that the water flow can be dispersed as much as possible. The bottom elevation of the overflow port 4 is 2016m. According to the weir flow formula, the flow coefficient is approximately 0.385, and the expected discharge flow is 6700m 3 / s, the weir top head is about 11m, so the water level in the shaft is expected to be about 2027m, which is lower than the top elevation of shaft 3, which can ensure that shaft 3 maintains a free water surface.

[0049] The drainage channel 5 is flat-bottomed. The bottom elevation of the drainage channel 5 is the same as that of the bottom of the downstream river channel 6, which is 1983m. The width is the same as the width of the overflow port 4, which is 68m. The average width of the river channel 6 is 125m. The discharge flow of the river channel 6 under the diversion tunnel 1 is 6700m. 3 / s, the corresponding water level is 2030m, the riverbed elevation is about 1983m, and the length of river channel 6 is about 900m.

[0050] The incoming flow from the diversion tunnel 1 enters the inlet section 2, which is located at an eccentric position of the vertical shaft 3 and has a certain bottom slope. When the water flows into the vertical shaft 3, it rotates downward along the wall of the shaft. When the water flows to the bottom plate of the vertical shaft 3, it begins to rotate upward. During this process, a swirling flow pattern with low flow velocity in the center and high flow velocity around will be formed in the vertical shaft 3. The friction resistance of the vertical shaft 3 wall and the shear pulsation of the vortex will greatly eliminate the kinetic energy of the water flow; then it overflows into the drainage channel 5 through the overflow port 4 and finally enters the downstream river channel 6. Since the central angle of the overflow port 4 is 180°, the length of the flow front is about 6 times the width of the diversion tunnel 1. Therefore, after the energy dissipation of the vertical shaft 3 and the dispersion and guidance of the overflow port 4, the residual energy of the water flow is very small, and the flow rate into the river channel 6 is significantly reduced.

[0051] Comparative Example

[0052] The inlet floor elevation of diversion tunnel 1 of a large hydropower station project is 2015m, the outlet floor elevation is 2013m, the total length is approximately 1550m, and the bottom slope is 0.13%. Diversion tunnel 1 is a gate tunnel section with cross-sectional dimensions of 17m×19m, a top arch central angle of 120°, and a cross-sectional area of ​​298.74㎡. The maximum design flow rate of diversion tunnel 1 is approximately 6700m 3 / s, the average flow velocity at the corresponding section is 22.4m / s, the intersection angle between the outlet section axis and the river channel 6 is approximately 53°, the width of the river at the outlet section is approximately 90m-130m, and the thickness of the riverbed cover is approximately 30m (the lower limit elevation of the strongly weathered bedrock is approximately 1983m). The diversion tunnel 1 outlet does not have the aforementioned vertical shaft structure, and the diversion tunnel 1 is directly connected to the downstream river channel 6.

[0053] Numerical calculations of hydrodynamics were conducted on the diversion tunnel and the downstream river channel. The plane flow field of the downstream river channel in the comparative example where the diversion tunnel outlet section was not equipped with the vertical shaft structure is shown as follows: Figure 4 、 Figure 5 As shown; after the vertical shaft structure is set at the outlet section of the diversion tunnel of the embodiment, the plane flow field of the downstream river channel is as follows Figure 6 、 Figure 7 shown. Figure 4 and Figure 6 The numbers on the median line represent the flow rate value. Figure 4 、 Figure 5 As can be seen from the figure, the direct outflow from the diversion tunnel in the comparative example has a great impact on the downstream river channel. The opposite bank is in a high velocity area. At 600m downstream of the diversion tunnel outlet, the bank slope velocity can reach 10m / s, and the pressure and scope of protection are both large. Figure 6 、 Figure 7 As can be seen, after installing the vertical shaft structure at the diversion tunnel outlet in the embodiment, the outflow velocity is significantly reduced, with the flow velocity on the opposite bank being only 2 m / s. There is no high-velocity zone in the downstream river channel, and protection of the downstream river channel is essentially unnecessary. This invention effectively solves the energy dissipation and anti-scour issues in the diversion tunnel outlet river channel.

[0054] The contents illustrated in the above embodiments should be understood as these embodiments are only used to more clearly illustrate the present invention, and are not used to limit the scope of the present invention. After reading the present invention, various equivalent modifications of the present invention by those skilled in the art shall fall within the scope defined by the claims attached to this application.

Claims

1. A diversion tunnel outlet shaft energy dissipation structure, comprising a shaft (3), an inlet section (2), and a diversion tunnel (1), characterized in that: The bottom of the vertical shaft (3) is provided with a bottom plate, and the bottom of the vertical shaft (3) is a closed structure. An inlet (7) and an overflow port (4) are provided on the wall of the vertical shaft (3). One end of the inlet section (2) is connected to the inlet port (7), and the other end of the inlet section (2) is connected to the diversion hole (1). The center line of the inlet port (7) in the width direction is eccentric to the vertical axis of the vertical shaft (3). The bottom elevation of the overflow port (4) is between the elevation of the bottom plate of the inlet section (2) and the elevation of the top plate of the inlet section (2). The horizontal cross-section of the vertical shaft (3) is circular, and the side wall of the inlet section (2) is tangent to the wall of the vertical shaft (3); The radius of the horizontal cross section of the vertical shaft (3) is 1.5-2 times the width of the inlet section (2); The bottom plate of the inlet section (2) has a downward slope, and the slope ranges from 5% to 15%; The depth of the vertical shaft (3) is 1-2 times the height of the inlet section (2).

2. The diversion tunnel outlet shaft energy dissipation structure according to claim 1, characterized in that: The length of the inlet section (2) is more than 10 times the width of the diversion hole (1).

3. The diversion tunnel outlet shaft energy dissipation structure according to claim 1, characterized in that: The overflow port (4) is an annular opening arranged on the wall of the vertical shaft (3) toward the river channel (6).

4. The energy dissipation structure of the diversion tunnel outlet shaft according to claim 3, characterized in that: The central angle of the annular opening ranges from 90° to 180°.

5. The energy dissipation structure of the diversion tunnel outlet shaft according to any one of claims 1 to 4, characterized in that: It comprises a drainage channel (5), wherein the drainage channel (5) is connected to the overflow port (4).

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