A method for determining the range of the pressure slope ratio at the inlet of the lower horizontal tunnel of a swirl vertical shaft based on numerical simulation

Abstract

The present invention discloses a method for determining the slope reduction rate range of the inlet of the lower horizontal tunnel of a swirling vertical shaft based on numerical simulation, belonging to the technical field of hydrodynamic mathematical simulation for urban flood control and drainage. First, an index representing the magnitude of slope reduction is proposed: the slope reduction rate. Since the reasonable value range of the unknown slope reduction rate is not known, different slope reduction rates can be set, and the reservoir water level H and the outlet velocity v of the slope reduction at each operating condition are extracted. Then, the relationship curves of water level ~ slope reduction rate and energy dissipation rate ~ slope reduction rate are established. By referring to the curve charts, the reasonable slope reduction rate range is determined. Finally, slope reduction rate values within the range are randomly selected for simulation calculation, and the calculation results are compared with the results obtained from chart query to verify the feasibility of the reasonable slope reduction rate range. The present invention can not only stabilize the flow pattern of water with a large discharge slope ratio and high velocity flowing through the lower horizontal tunnel, but also ensure smooth ventilation at the top of the lower horizontal tunnel, avoiding the "blocked tunnel" of mountain floods.

Description

Technical Field

[0001] The present invention belongs to the technical field of hydrodynamic mathematical simulation for urban flood control and drainage, and particularly relates to a method for determining the range of the slope reduction rate at the inlet of the horizontal tunnel under the swirl shaft based on numerical simulation. Background Art

[0002] Many cities in our country are built along water, with mountains on the back and the sea in front, having steep slopes and rapid flows. Mountain torrents are extremely likely to rush into the urban area, causing urban waterlogging. As a new type of water discharge channel, the swirl shaft is an ideal hydraulic structure for discharging mountain torrents from high places in the city to low-lying inland rivers or outside the city, and can effectively solve the problem of urban flood control and waterlogging. However, the swirl shaft usually has technical problems such as a large discharge gradient, high flow velocity, variable directions of the tunnel alignment, and extremely complex internal water flow conditions. Especially at the connection section between the shaft and the horizontal tunnel, due to the close to vertical nesting of the shapes, on the one hand, the sudden change in the water flow direction in the shaft directly affects the water flow pattern in the horizontal tunnel and its connection flow pattern with the river at the outlet; on the other hand, there are uneven turbulent three-axis vortices at the connection between the shaft and the horizontal tunnel, and the water flow violently impacts, tumbles, and turbulences, exacerbating the vibration of the entire tunnel and causing harm to the structure of the entire unpressurized tunnel of the shaft; furthermore, the shape of the connection section affects the energy dissipation effect in the tunnel.

[0003] Usually, a slope reduction is set at the top of the horizontal tunnel at the connection to stabilize the flow. However, hydraulic elements such as the overall flow pattern of the swirl shaft, the pressure on the bottom slab of the plunge pool, the flow velocity, and the energy dissipation rate are very sensitive to the degree of change of the slope reduction. If no slope reduction is set or the slope reduction rate is too small, the connection is the main place for energy dissipation, and most of the energy can be dissipated. However, an overly high energy dissipation rate may not necessarily be an advantage, because it will lead to a decrease in the flow velocity, poor flow pattern in the tunnel, generation of hydraulic jumps, rising of the water surface, alternation of open-channel and full-flow, resulting in obstruction of ventilation at the tunnel top, reduction of the flow velocity, causing the problem of "water choking" in the water flow, affecting mountain torrent discharge, the stress state of the tunnel, and energy dissipation at the outlet, etc.; if the slope reduction rate is too large, the flow velocity at the outlet of the slope reduction can be increased, suppressing energy dissipation, and the water surface line in the tunnel drops, but it will also cause the cross-section of the horizontal tunnel to shrink too much, affecting the flow capacity, and unstable swinging of the rotating vortex band in the shaft, surging waves in the bending section, increasing water pressure and flow velocity in the tunnel, etc., thus inducing problems such as wall cavitation and damage to the concrete structure.

[0004] Each time the slope reduction rate is adjusted by means of a hydraulic physical model, it will consume a large amount of manpower, material resources, and financial resources, and is limited by objective conditions such as weather, instruments, working cycles, and sites, inevitably causing waste of time and materials. By using the mathematical model means, after mutual coupling verification and good agreement with the physical model, multiple computers can be used to calculate multiple slope reduction schemes in parallel at the same time, which is more suitable for in-depth study of the slope reduction rate problem. A relationship curve table is made, and in the way of looking up the table, the reasonable range of the slope reduction rate size is determined, providing a scientific basis for the design of the swirl shaft. Looking up the table can also avoid too many physical and numerical model runs. Summary of the Invention

[0005] (1) Technical problems to be solved

[0006] A reasonable slope at the inlet of the lower horizontal tunnel plays an important "connecting the upper and the lower" role. However, too large or too small a slope rate will directly affect the hydraulic characteristics of the entire vertical shaft, and further affect its safe and stable operation. When using the hydraulic physical model method, the slope size needs to be adjusted manually many times. It often takes several days for the model to be firm before starting the test. Sometimes it is also restricted by objective conditions such as weather, instruments, working cycles, and sites, resulting in waste of time and materials. To solve the above technical problems, based on the mathematical model, different slope schemes are calculated, the relationship curves between the reservoir water level and the slope rate, and the energy dissipation rate and the slope rate are established. By using the method of checking the curve charts and combining with the flow pattern distribution, a reasonable range of slope rates is determined and its feasibility is verified.

[0007] (2) Technical solution

[0008] To solve the above technical problems, the present invention provides a method for determining the range of the slope rate at the inlet of the lower horizontal tunnel of a swirl vertical shaft based on numerical simulation. A three-dimensional mathematical model is established. Since the reasonable value range of the unknown slope rate is not known, different slope rates can be set. The reasonable range of slope rates is determined by using the relationship charts between the slope rate and the reservoir water level, and the slope rate and the energy dissipation rate, and its feasibility is verified. The specific steps are as follows:

[0009] a. Collect the design data of the plan and profile of the swirl vertical shaft, the basic design data such as the hydrology, geology, project classification, flood standard, and general project layout after the construction of the vertical shaft, as well as the gate operation plan;

[0010] b. According to the collected design data, establish a three-dimensional hydrodynamic mathematical model of the swirl vertical shaft, analyze the hydrological data and the gate operation plan, and propose an index representing the slope size: the slope rate;

[0011] c. Calculate the energy dissipation rate under each operating condition;

[0012] d. According to the theoretical value of the reservoir water level, determine the reasonable range of slope rates by using the method of checking the relationship curve table;

[0013] e. Specifically take values within the range of slope rates, numerically simulate and calculate its discharge capacity, energy dissipation rate, flow pattern distribution, and the flow velocity at the slope outlet, etc., and compare with the relationship curve table to verify the feasibility of the reasonable range of slope rates.

[0014] Preferably, the slope rate calculation formula is as shown in the following formula:

[0015]

[0016] In the formula, b is the width of the slope outlet, h is the height of the slope outlet, and A0 is the cross-sectional area of the lower horizontal tunnel at the slope outlet. The simulation calculations are carried out for various operating conditions;

[0017] Preferably, the energy dissipation rate calculation formula is as follows:

[0018]

[0019] In the formula, H D is the bottom elevation of the outlet of the slope-suppressing section; when the flow at the outlet of the slope-suppressing section is pressurized flow, h′ = h, and when the flow at the outlet of the slope-suppressing section is unpressurized flow, it is the water depth; H is the reservoir water level. The approach velocity in the reservoir area is very small and can be ignored. The relationship curves of water level and slope-suppressing rate, and energy dissipation rate and slope-suppressing rate are established.

[0020] (3) Beneficial effects

[0021] The beneficial effects of the present invention: The present invention proposes an index characterizing the size of the slope-suppressing section: the slope-suppressing rate, and establishes the relationships between the slope-suppressing rate and the reservoir water level, and between the slope-suppressing rate and the energy dissipation rate. According to the theoretical value of the reservoir water level, by referring to the relationship curve table, a reasonable range of the slope-suppressing rate is determined, which can not only stabilize the flow pattern of the water flow with a large discharge slope ratio and high velocity flowing through the lower horizontal tunnel, but also ensure smooth ventilation at the top of the lower horizontal tunnel, avoid "choking the tunnel" by mountain floods, and provide technical services for the construction, operation and management of the swirl shaft. Description of the drawings

[0022] Figure 1 is the overall three-dimensional mathematical model of the swirl shaft tunnel;

[0023] Figure 2 is the mesh division diagram of the swirl shaft tunnel;

[0024] Figure 3 is the schematic diagram of the slope-suppressing scheme at the inlet of the lower horizontal tunnel;

[0025] Figure 4 is the relationship curve of water level ~ slope-suppressing rate under various operating conditions of the swirl shaft tunnel;

[0026] Figure 5 is the relationship curve of energy dissipation rate ~ slope-suppressing rate under various operating conditions of the swirl shaft tunnel;

[0027] Figure 6 is the flow pattern distribution diagram of the lower horizontal tunnel under the condition of the slope-suppressing rate m = 59.00% in working condition 2;

[0028] Figure 7 is the streamline distribution diagram of the lower horizontal tunnel under the condition of the slope-suppressing rate m = 59.00% in working condition 2. Specific implementation manners

[0029] The technical solutions in the embodiments of the present invention will be further clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0030] Embodiment 1

[0031] The present invention provides a method for determining the slope ratio range of the inlet of the lower horizontal tunnel of a swirl vertical shaft based on numerical simulation. A three-dimensional mathematical model is established, different slope ratios are set, and a reasonable slope ratio is determined by using the relationship charts between the slope ratio and the discharge capacity, and between the slope ratio and the energy dissipation rate. The specific calculation method includes the following: First, collect the design data of the plan and profile of the swirl vertical shaft, the basic design data such as the hydrology, geology, engineering classification, flood standard, and general layout of the project after the construction of the vertical shaft, as well as the gate operation plan; Second, according to the collected design data, establish a three-dimensional hydrodynamic mathematical model of the swirl vertical shaft, analyze the hydrological data and the gate operation plan, and propose an index representing the slope size: the slope ratio where b is the width of the slope outlet, h is the height of the slope outlet, and A0 is the cross-sectional area of the lower horizontal tunnel at the slope outlet. Perform simulation calculations for various operating conditions; Then, according to the theoretical value of the reservoir water level, determine the reasonable slope ratio range by referring to the relationship curve table. Finally, specifically select values within the slope ratio range, and perform numerical simulation calculations on its discharge capacity, energy dissipation rate, flow pattern distribution, and the flow velocity at the slope outlet, etc., and compare with the relationship curve table to verify the feasibility of the reasonable slope ratio range.

[0032] Specifically, taking the flood diversion tunnel of the Sanxi Reservoir in Fuzhou Binhai New City as an example for illustration, a three-dimensional mathematical model is established using FLUENT, as Figure 1 . The upper boundary of the model is taken about 40 m upstream of the inlet control gate of the flood diversion tunnel, and the lower boundary is taken about 100 m downstream of the river channel of the apron. The upstream reservoir entrance adopts a velocity inlet boundary, and the downstream outlet adopts a free outflow boundary. The normal velocity is given as zero and the no-slip condition is given on the solid wall. The standard wall function is used to process the viscous sublayer near the wall. Considering that part of the calculation area is regular and part is irregular, a hybrid grid combining structured tetrahedral grids and unstructured hexahedral grids is adopted, and local encryption is performed at key positions. The number of grid cells in the model is 1,781,485, and the number of nodes is 1,066,532. The grid division is as Figure 2 . To accelerate the calculation speed, the initial flow field is set to be filled with water below a certain water level in the reservoir area and filled with air above it. The model simulates 13 operating conditions of the inlet sluice, which are respectively

[0033] Condition 1: Holes 1# to 4# are opened, and the discharge is 163 m 3 / s;

[0034] Condition 2: Holes 1# to 4# are opened, and the discharge is 142 m 3 / s;

[0035] Condition 3: Holes 1# to 4# are opened, and the discharge is 125 m 3 / s;

[0036] Condition 4: Holes 1# to 4# are opened, and the discharge is 90 m 3 / s;

[0037] Operating condition 5: Holes 1# to 4# are open, and the discharge is 60 m 3 / s;

[0038] Operating condition 6: Holes 2# to 4# are open, and the discharge is 142 m 3 / s;

[0039] Operating condition 7: Holes 2# to 4# are open, and the discharge is 132 m 3 / s;

[0040] Operating condition 8: Holes 2# to 4# are open, and the discharge is 125 m 3 / s;

[0041] Operating condition 9: Holes 2# to 4# are open, and the discharge is 112 m 3 / s;

[0042] Operating condition 10: Holes 2# and 3# are open, and the discharge is 142 m 3 / s;

[0043] Operating condition 11: Holes 2# and 3# are open, and the discharge is 125 m 3 / s;

[0044] Operating condition 12: Holes 2# and 3# are open, and the discharge is 102 m 3 / s;

[0045] Operating condition 13: Holes 2# and 3# are open, and the discharge is 90 m 3 / s.

[0046] Taking the flood diversion tunnel of Sanxi Reservoir in Fuzhou Binhai New City as an example, the project is located in the Sanxi Basin. By excavating a tunnel in the mountain on the right bank of the auxiliary dam of Sanxi Reservoir, the flood (Q = 142 m 3 / s) below 30 years in Sanxi Reservoir is discharged into Nanyang Qixi River through the flood diversion tunnel of Sanxi Reservoir and directly discharged into Waiwenwu Reservoir through Jiangtian New River. The hydraulic elements such as the overall flow pattern, pressure, flow velocity, and energy dissipation rate of the tunnel are very sensitive to the degree of slope change. Therefore, an index representing the size of the slope is proposed: slope rate In the formula, b is the width of the slope outlet, h is the height of the slope outlet, and A0 is the cross-sectional area of the lower horizontal tunnel at the slope outlet. Through the technical means of physical and numerical model coupling, since the reasonable value range of the slope rate is unknown, five schemes with slope rates of 0.00%, 43.48%, 61.89%, 65.90%, and 72.92% can be set. The schematic diagram of the slope scheme is as shown in Figure 3 .

[0047] The water level - slope rate relationship curve is as shown in Figure 4 . When the slope rate in operating condition 1 is 72.92%, it is orifice flow, and the other schemes are weir flow. The flow rates in operating conditions 4, 5, 12, and 13 are less than 102 m 3 / s, the slope reduction rate has basically no influence on the reservoir water level; for other working conditions, the flow rate is greater than 102 m 3 / s. The reservoir water level rises as the slope reduction rate increases, and when the slope reduction rate is greater than 61.89%, the increase amplitude of the reservoir water level becomes larger.

[0048] The relationship curve of energy dissipation rate ~ slope reduction rate is as Figure 5 . When the slope reduction rate is constant, the energy dissipation rate decreases as the flow rate increases. When the flow rate is constant, as the slope reduction rate increases, the constraint effect of the slope on the water flow is enhanced, the inhibitory effect on the violent tumbling and strong turbulence of the water flow is enhanced, and the water flow is converted from pressure energy into kinetic energy of the water flow, playing a role in stabilizing the flow, and the energy dissipation rate decreases accordingly. The flow rates of working conditions 4, 5, 12 and 13 are less than 102 m 3 / s, and the slope size has little influence on the energy dissipation rate; for other working conditions, the flow rate is greater than 102 m 3 / s. Taking the slope reduction rate of 61.89% as the "critical point" of the energy dissipation rate reduction: when the slope reduction rate is less than 61.89%, the reduction amplitude of the energy dissipation rate is small; when the slope reduction rate is greater than 61.89%, the reduction amplitude of the energy dissipation rate increases, and thereafter the slope size has a great influence on the energy dissipation rate.

[0049] Taking all factors into consideration: (1) To avoid phenomena such as water flow disorder and excessive lateral water level difference beyond the straight wall range of the tunnel section in the plane bending section 24 m - 104 m away from the slope outlet, the slope reduction rate should not be too large or too small; (2) There is a stilling basin at the outlet of the lower horizontal tunnel, which means that energy dissipation is still required at the outlet. Then the energy dissipation rate at the slope should not be too large, otherwise the flow velocity will decrease too much, the cross-sectional area of the water flow will increase, squeezing the gas in the tunnel, and it is easy to cause the "blocked tunnel" of mountain floods. Therefore, the slope reduction rate should be on the larger side; (3) The flow velocity in the tunnel needs to meet the safety of the concrete structure and avoid cavitation, and the flow velocity does not exceed 25 m / s; (4) The flood discharge capacity of the sluice chamber takes working conditions 2 and 10 as the control working conditions. According to the theoretical values of the reservoir water levels of the two, query the relationship curve of water level ~ slope reduction rate, and the corresponding slope reduction rates are 58.24% - 61.95%. The reservoir water levels corresponding to each working condition are shown in Table 1. The relative error between the reservoir water levels with slope reduction rates of 58.24% - 61.95% and the theoretical values is 0 - 0.34%, meeting the flood discharge capacity. Then query the relationship curve of energy dissipation rate ~ slope reduction rate. The energy dissipation rates corresponding to each working condition are shown in Table 2. The energy dissipation rates at the slope outlet with slope reduction rates of 58.24% - 61.95% are 29.49% - 47.29%, which is 11.83% - 25.04% lower than that without slope. The flow velocities at the slope outlet of the control working conditions are 18.45 - 21.69 m / s, and the flow velocity range is relatively reasonable, and the energy dissipation rate range is reasonable. Therefore, the reasonable range of the slope reduction rate is 58.24% - 61.95%, and the slope reduction rate can be selected within this range according to the actual situation of the project.

[0050] Take the slope pressing rate of 59.00% within a reasonable range and conduct simulation calculations under working condition 2. The water level in the digital model calculation library is 63.51 m, the flow velocity at the slope pressing outlet is 20.68 m / s, and the energy dissipation rate is 30.97%. Querying the relationship curve, the corresponding water levels in the reservoir and the energy dissipation rate are 63.68 m and 33.97% respectively. The curve relationship table is consistent with the digital model results. The maximum lateral water level difference is 2.16 m, which is located in the plane bending section 43.66 m away from the slope pressing outlet. The water level is within the straight wall range, and the overall flow pattern distribution is relatively stable. The slope pressing rate of 59.00% is feasible. The flow pattern and streamline distribution are as shown in Figure 6 and Figure 7 .

[0051] Table 1 Comparison of the discharge capacity of the lock chamber with slope pressing rates of 58.24% - 61.95%

[0052]

[0053] Table 2 Comparison of the energy dissipation rates at the slope pressing outlets with slope pressing rates of 58.24% - 61.95%

[0054]

[0055]

[0056] The above-described embodiments only represent the preferred embodiments of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications, improvements, and substitutions can be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the appended claims.

Claims

1. A method for determining the range of the pressure slope rate at the inlet of the lower horizontal tunnel of a swirl vertical shaft based on numerical simulation, characterized in that Establish a three-dimensional mathematical model. Since the reasonable value range of the slope compression rate is unknown, different slope compression rates can be set. Use the relationship charts between the slope compression rate and the reservoir water level, and between the slope compression rate and the energy dissipation rate to determine the reasonable range of the slope compression rate and verify its feasibility. The specific steps are as follows: a. Collect the design data of the vertical section of the swirl shaft, the basic design data of hydrology, geology, project classification, flood standard, and general project layout after the construction of the shaft, as well as the gate operation plan; b. Based on the collected design data, establish a three-dimensional hydrodynamic mathematical model of the swirl shaft, analyze the hydrological data and the gate scheduling scheme, and propose an index representing the size of the slope suppression: the slope suppression rate , where is the width of the slope suppression outlet,[ the height of the slope suppression outlet,[ the cross-sectional area of the lower horizontal tunnel at the slope suppression outlet, and conduct simulation calculations for various operating conditions; c. Calculate the energy dissipation rate under each operating condition , where H D is the bottom elevation of the outlet of the pressure slope; When there is pressure flow at the outlet of the pressure slope , and when there is no pressure flow at the outlet of the pressure slope, it is the water depth; H is the reservoir water level, and the approach velocity in the reservoir area is very small and can be ignored. The relationship curves between water level and pressure slope rate, and between energy dissipation rate and pressure slope rate are established; d. According to the theoretical value of the reservoir water level, determine the reasonable range of the slope compression rate by referring to the relationship curve table; e. Specifically select values within the range of the slope compression rate, and numerically simulate and calculate its discharge capacity, energy dissipation rate, flow pattern distribution, and the flow velocity at the slope compression outlet, and compare with the relationship curve table to verify the feasibility of the reasonable range of the slope compression rate.

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