Hydraulic design method for guiding and energy dissipation of double-curved spillway

Abstract

The application provides a kind of double curved spillway guide energy dissipation hydraulic design method, belongs to the technical field of water conservancy and hydropower engineering, the application is the energy dissipation and flow guide design of double curved spillway under specific conditions, through the joint use of several kinds of flow guide energy dissipation works such as cylindrical energy dissipation pier+arc guide pier+energy dissipation pool+inclined sill+step, finally solve the flow guide and energy dissipation of double curved spillway Anti-scour problem, the method overcomes the problem that the conventional single flow guide energy dissipation mode is poor in improving effect due to the deterioration of water flow state caused by the superimposed influence of centrifugal force on short distance double curved water flow.

Description

Technical Field

[0001] This invention relates to a hydraulic design method for guiding and dissipating energy in a double-curved spillway, belonging to the field of water conservancy and hydropower engineering technology. Background Technology

[0002] According to the "Spillway Design Code" [1] (SL253-2018), the layout of the spillway should ensure smooth water flow, and the axis should preferably be straight. In the existing technology, many projects inevitably adopt the layout of bends or even double bends due to limitations such as terrain and construction conditions, in order to reduce damage to the ecological environment and save on project investment. Under the centrifugal force of the bend, the flow rate and water depth distribution are extremely uneven. The water surface in the bend will produce problems such as transverse slope and transverse shock waves. Especially when double bends are arranged in a short distance, the upstream bend water flow will have a superimposed effect on the downstream bend water flow, which will further cause the water flow pattern to deteriorate and inevitably affect the downstream energy dissipation and scour prevention. Therefore, it is necessary to study the factors that affect the water flow pattern and downstream energy dissipation effect of the double bend type spillway in order to improve the bend water flow pattern and improve the downstream energy dissipation effect. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a hydraulic design method for guiding and dissipating energy in a double-curved spillway, comprising the following steps:

[0004] (1) A group of cylindrical energy dissipation piers is arranged at the inlet of the spillway to adjust the uneven inflow at the inlet;

[0005] (2) The first counterclockwise bend is provided after the energy dissipation pier group. The bottom of the first counterclockwise bend is designed to be gradually widened so that the water flow can be fully diffused and the unit width flow rate can be reduced. An arc-shaped guide pier is designed at the center line of the first counterclockwise bend to divide the inflow into two parts to prevent the water flow from concentrating in the first counterclockwise bend.

[0006] (3) A first energy dissipation pool is set after the first counterclockwise bend. The tail sill of the first energy dissipation pool adjusts and dissipates the water flow in the first counterclockwise bend, and balances the water flow distribution on the left and right banks.

[0007] (4) A second clockwise bend is set after the first stilling basin. The bottom slope of the second clockwise bend is 1:4. The water flow is also affected by centrifugal force, and the discharged water flow is biased to the concave bank side, resulting in an uneven water flow distribution. A sloping bottom sill is designed in the second clockwise bend to adjust the water flow balance. The top of the sloping bottom sill has a small rounded chamfer on the water surface to prevent the water flow from leaving the boundary and making a leap.

[0008] (5) A straight section of the discharge channel is set after the second clockwise bend. Unequal width steps are set on the straight section of the discharge channel. The water flows through the steps, which intensifies the rolling and collision between water bodies, further dissipates energy, and reduces the flow velocity.

[0009] (6) A second energy dissipation pool is set after the straight channel step to dissipate energy and stabilize waves, and guide the water flow smoothly into the discharge culvert.

[0010] Preferably, in step (1), the ideal flow velocity V to be reached by the water flow after initially planning a group of stilling piers is determined. l The average water depth H at the spillway inlet is calculated by subtracting a certain safety freeboard from the height of the spillway sidewall. The average flow velocity V at the inlet section is measured, and the required flow width B is calculated based on the discharge flow rate Q. The net spacing b between single-row stilling piers is calculated, where B = (n-1)b, and n is the number of stilling piers in a single row. The height of the stilling piers is determined based on the average water depth H. The spacing between stilling pier rows is S = (1.0~1.2)b, with the front and rear rows of stilling piers arranged in a staggered, quincunx pattern. After testing the average flow velocity V2 behind the stilling pier group, the net spacing b2 between the stilling piers is readjusted based on the magnitude of V2, and the number of stilling piers n2 and the row spacing S2 are adjusted accordingly. The average flow velocity V3 behind the stilling piers is then tested, and this process is repeated until V2 is reached. n ≈V1, adjust to achieve the ideal arrangement of stilling piers; in addition, the spacing between stilling piers in a single row can be adjusted to be of unequal width according to the unbalanced ratio of the inflow, and the net spacing b value of stilling piers is smaller at the location with larger flow.

[0011] Preferably, in step (2), the width ratio of the inlet and outlet of the first counterclockwise bend is 1.5 to 1.7, and an arc-shaped guide pier is designed at the centerline of the first counterclockwise bend, with a radius r = R, where R is the radius of curvature of the bend's centerline; width b 墩 =Minimum structural width; the pier width should be as small as possible to avoid occupying the flow passage width and save on project investment; length l = length of the curve centerline; the head of the arc-shaped guide pier is designed with a streamlined shape and the radius of the connecting line is r. 流 =1.71b 墩 The streamline length is l 流 =1.21b 墩 The tail is designed as a semicircle, with a diameter d = b. 墩 The streamlined head can effectively divide the water flow and will not cause local water level rise at the pier head.

[0012] Preferably, in step (3), the first stilling basin is designed as a sill-type stilling basin with no submerged outflow downstream, and the length of the first stilling basin is L. k = (0.7~0.8)L j L j Given the length of the free hydraulic jump, the height of the tail sill of the first stilling basin is c = h. c-H1, h c "H1 is the water depth after the jump, and H1 is the water depth at the top of the tail sill."

[0013] Preferably, in step (4), the maximum height h of the sloping sill is 1 / 10h. i h i The maximum water depth of the bend; there is a certain distance s between the sloping bottom rails, generally s = 10 to 12h; the top of the sloping bottom rail has a slope i from the concave bank to the convex bank, generally the slope i = 1:100 to 1:300; the sloping bottom rail and the centerline of the bend have a certain angle θ, generally the angle θ = 30° to 60°.

[0014] Preferably, in step (5), maintaining a cascading flow pattern during the stage is necessary to ensure a high energy dissipation rate and control d. c / h < 0.0916 (h / l) -1.276 d c Let h be the critical water depth, h be the step height, and l be the step length.

[0015] Preferably, in step (6), the second stilling basin is designed as a submerged type, and the length of the second stilling basin is L. k = (0.7~0.8)L j L j The length of the free hydraulic jump, and the height of the tail sill of the second stilling basin, c = h. c -H1, h c "H1 is the water depth after the leap), and H1 is the water depth at the top of the tail sill."

[0016] This invention provides a hydraulic design method for guiding and dissipating energy in a double-curved spillway. It addresses the energy dissipation, scour prevention, and flow guidance design of double-curved spillways under specific conditions. This method overcomes the problem that conventional single-method energy dissipation approaches suffer from poor flow regulation due to the cumulative effects of flow deterioration in short-distance double-curved spillways. Compared to existing technologies, the technical solution of this invention has at least the following advantages: This invention utilizes a combination of cylindrical stilling piers, arc-shaped guide piers, stilling basins, sloping sills, and steps to ultimately solve the flow guidance and energy dissipation / scour prevention problems of double-curved spillways. This combined use of energy dissipation structures provides the following advantages:

[0017] 1. Existing single-function energy dissipation structures are insufficient to address complex boundary flow problems. By fully leveraging the advantages of each individual energy dissipation structure, the combined application of a series of guiding energy dissipation measures, such as balanced inflow at stilling piers, bend guidance at guide piers, energy dissipation in stilling basins, bend guidance at sloping bottom sills, and energy dissipation at straight channel steps, has improved the severe flow conditions caused by the superposition of centrifugal forces in the double bends. This has eliminated the enormous energy generated by the nearly 60m head difference in the flood discharge, successfully resolving the hydraulic problem of the connection between the natural gully spillway and the underground culvert's double-bend spillway.

[0018] 2. Structurally, the spillway adopts a sloping sill design for guiding the flow in the sharp bends: the top of the sloping sill is designed with a certain slope to guide the concentrated water flow on the concave bank to the convex bank; the edges of the sloping sill's cross-flow surface are rounded to prevent the water flow at the top of the sill from detaching from the boundary and leaping, which greatly improves the flow pattern in the bend and perfectly solves the problem of water flow concentration caused by centrifugal force in the sharp bends. Attached Figure Description

[0019] Figure 1 A three-dimensional schematic diagram of the overall structure of a double-curved spillway guiding energy dissipation system designed according to the present invention for a reservoir spillway in Fuzhou.

[0020] Figure 2 Detailed drawing of the first curve energy dissipation structure combining a bend energy dissipation pier, a guide pier, and an energy dissipation pool.

[0021] Figure 3 Detailed drawing of the second curved sloping bottom sill guiding and energy dissipation structure designed in this invention.

[0022] Figure 4 Detailed diagram of the combined flow diversion and energy dissipation structure of the straight discharge channel steps and stilling pool designed in this invention.

[0023] The attached diagram is labeled as follows: 1-Cylindrical stilling basin group, 2-Arched guide pier, 3-First stilling basin, 4-Tail sill of the first stilling basin, 5-Sloping bottom sill, 6-Straight discharge channel, 7-Steps of unequal width, 8-Second stilling basin. Detailed Implementation

[0024] The present invention will now be described in detail with reference to the accompanying drawings.

[0025] Example 1

[0026] This patent is based on a physical model test of a reservoir in a certain project. This project is a small (Class II) reservoir primarily for irrigation, but also for flood control and water supply. The reservoir's main structure consists of a dam and a spillway. The dam is a concrete-faced rockfill dam with a maximum height of 22.50m. The spillway is a side channel type located on the left bank of the dam, with a wide-crested weir at the inlet, without gate control. A steep slope section of the natural gully spillway is immediately following the weir. An intercity railway passes through the reservoir's spillway, partially occupying the lower section. Temporary flood control measures were implemented during construction, with permanent modifications to follow later. The hydraulic design method for guiding the water flow and dissipating energy in this temporary flood control channel employs a combined energy dissipation structure of cylindrical stilling piers, stilling basins, sloping sills, and stepped surfaces.

[0027] The water flow conditions in this project are relatively complex. The inlet is a broad-crested weir without gate control. Immediately after the weir is a steep section of a natural gully spillway. The intercity railway crosses the reservoir spillway, partially occupying the lower section. A large platform is poured on top of the railway section crossing the spillway, requiring the temporary flood discharge channel to bypass this platform, necessitating a double-bend section. This results in turbulent and poorly shaped water flow.

[0028] (1) The average flow velocity at the inlet section was measured to be 3.0 m / s. Based on the flood discharge rate of 24 m³ / s... 3 / s, average water depth H=2.2m, the required flow width B=3.6m is calculated and determined, the net spacing of a single row of stilling piers b=1.2m, B=3.6m=(4-1)×1.2; 4 rows of 14 cylindrical stilling piers are set at the inlet of the temporary flood discharge channel to balance the flow;

[0029] (2) The first counterclockwise curve is located at the bottom of the railway top platform section and is designed to gradually widen. The inlet width of the curve is 6m, the outlet width is 12m, and the inlet-outlet width ratio is 1.0 to 2.0. An arc-shaped guide pier 2 is designed at the centerline of the curve: the radius of the arc-shaped guide pier 2 is r = R = 27.0m; the width of the pier is b = 0.8m, and the pier width should be as small as possible to avoid occupying the flow width and to save on project investment; the length is l = the length of the curve centerline; the head of the arc-shaped guide pier 2 is designed with a streamlined shape and a connecting line radius r. 流 =1.71 × 0.8 = 1.37 m, streamline length is l 流 =1.21×0.8=0.97m, the tail is designed as a semicircle, the diameter of the semicircle d=0.8m. The arc-shaped guide pier 2 divides the water flow in the bend into two parts, reducing the uneven water flow distribution caused by the centrifugal force of the bend;

[0030] (3) A first stilling basin 3 is set at the junction of the double bends, with a tail sill 4 at a height of 1.2m. The first stilling basin 3 is designed as a sill-type stilling basin with no submerged outflow downstream. The length Lk of the first stilling basin 3 is 0.8 times L. jThe length is 14m, and the height of the tail sill 4 of the first stilling basin is c = 1.2m. The first stilling basin 3 adjusts and dissipates energy in the bend, balancing the water flow distribution on the left and right banks;

[0031] (4) The water flow over the energy dissipation sill enters the second clockwise bend. The bottom slope of the second bend is 1:4. The water flow in the bend is also affected by centrifugal force, and the downstream water flow is biased towards the concave bank, resulting in an uneven water flow distribution again. The maximum height of the sloping bottom sill 5 is h = 1 / 10 × 1.6 = 0.16; the sill distance is s = 12 × 0.16 ≈ 2.0m; the top of the sloping bottom sill 5 has a slope i = 1:225 from the concave bank to the convex bank; the sloping bottom sill 5 has a certain angle θ = 40°~43° with the centerline of the bend; the top of the sloping bottom sill 5 has a small rounded chamfer on the water surface to prevent the water flow from leaving the boundary and making a leap. The guiding and energy dissipation effect of the sloping bottom sill 5 is obvious. The water flow is evenly distributed throughout the entire bend section, and there is no local bottom plate flow interruption. The water surface presents a wave-like leaping motion.

[0032] (5) After the adjusted water flow enters the straight section of the spillway 6, the water flow undergoes energy dissipation through stepped cascades. The first 5 steps are designed as level steps with a uniform slope of h = 0.6 m and l = 2.5 m. The subsequent steps are designed as steps of unequal height due to the terrain. The energy is further dissipated through the steps, and the energy of the water flow decreases at the bottom stilling basin.

[0033] (6) A second stilling basin 8 is set after the straight channel step to dissipate energy and stabilize waves. The second stilling basin 8 is designed as a submerged type, and the length of the basin is L according to the hydraulic design of the stilling basin. k =7m, the height of the tail sill of the second stilling basin is c=0.65m, guiding the water flow smoothly into the spillway culvert.

[0034] This invention patent solves the problems of water flow guidance and energy dissipation and scour prevention in double-curved spillways by combining several flow diversion and energy dissipation structures, such as cylindrical energy dissipation piers, arc-shaped flow diversion piers, energy dissipation pools, sloping bottom sills, and steps.

[0035] The embodiments described above are merely preferred embodiments of the present invention, and are described in a relatively specific and detailed manner. However, the present invention is not limited to these embodiments. It should be noted that for those skilled in the art, any modifications made without departing from the spirit of the present invention fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A method of hydraulic design of a double-curved spillway with guidance and energy dissipation, characterized in that, It comprises the following steps: (1) The cylindrical group of flow straightener is arranged at the entrance of spillway to adjust the uneven inflow of natural gully spillway; the ideal flow velocity V l of the water flow after the initial group of flow straightener is reached; the height of the spillway side wall minus a certain safety superhigh is the average water depth H of the spillway entrance; the average flow velocity V of the entrance section is measured, and then the required flow width B and the net distance b of the single-row flow straightener are determined according to the discharge flow Q, B=(n-1) b, and n is the number of single-row flow straighteners; the height of the flow straightener is determined according to the average water depth H; the row distance S of the flow straightener is (1.0~1.2) b, and the front and rear rows of flow straighteners are staggered in a plum blossom type; the average flow velocity V2 of the water flow after the group of flow straighteners is tested by experiment, the net distance b2 of the flow straighteners is adjusted according to the size of V2, and the number n2 and the row distance S2 of the flow straighteners are adjusted accordingly; the average flow velocity V3 of the water flow after the flow straighteners is tested again, and the ideal arrangement type of the flow straighteners is adjusted by repeating the above steps; in addition, the distance of the single-row flow straighteners is adjusted to be of unequal width according to the uneven ratio of the inflow flow, and the value of the net distance b of the flow straighteners at the position with larger flow is smaller. (2) The first counterclockwise bend is arranged behind the group of baffle blocks, the bottom of the first counterclockwise bend is designed to be gradually expanded horizontally to make the water flow fully spread and reduce the single-width flow, an arc-shaped guide block is arranged at the center line of the first counterclockwise bend to separate the inflow into two parts to prevent the water flow in the first counterclockwise bend from being concentrated; The first counterclockwise bend import and export width ratio is 1.5-1.7, an arc flow guide pier is designed at the center line of the first counterclockwise bend, the arc flow guide pier radius r=R, R is the bend center line curvature radius; width b 墩 =minimum structure width, the pier width should be as small as possible to avoid occupying the flow width and saving engineering investment; length l=bend center line length; the head of the arc flow guide pier is designed to be streamline type, the connecting line radius is r 流 =1.71b 墩 , the streamline length is l 流 =1.21b 墩 , the tail is designed to be a semicircle, the semicircle diameter d=b 墩 , the streamline head can better divide the water flow and will not cause the phenomenon of local water level high at the pier head; (3) The first counterclockwise bend is followed by a first stilling basin, and the tail sill of the first stilling basin adjusts and dissipates the water flow in the first counterclockwise bend, balancing the water flow distribution on the left and right banks; the first stilling basin is designed as a submerged outlet downstream of a sill-type stilling basin, and the length L of the first stilling basin is (0.7-0.8)L k . j L j is the length of a free water jump, the height c of the tail sill of the first stilling basin is h c -H1, h c " is the post-jump water depth, and H1 is the water depth at the top of the tail sill. (4) The first stilling basin is provided with a second clockwise bend, the bottom slope of the second clockwise bend is 1:4, the water flow is simultaneously affected by the centrifugal force, the discharged water flow is biased to the concave bank side, the water flow distribution is again unbalanced, a slanting bottom sill is designed in the second clockwise bend to adjust the water flow balance of the second clockwise bend; the top of the slanting bottom sill has a circular arc small chamfer, which prevents the water flow from jumping out of the boundary; the maximum height h of the slanting bottom sill is 1 / 10 h i , h i is the maximum water depth of the bend; the slanting bottom sills have a certain sill distance s, the sill distance s is 10~12h; the top of the slanting bottom sill has a slope i that is inclined from the concave bank to the convex bank, the slope i is 1:100~1:300; the slanting bottom sill has a certain included angle θ with the center line of the bend, the included angle θ is 30°~60°; (5) The straight section spillway is arranged behind the second clockwise bend, unequal-width steps are arranged on the straight section spillway, the water flow intensifies the rolling and collision between water bodies through the steps, further kills the energy, and reduces the flow rate; (6) The second stilling basin is arranged behind the step, energy is dissipated and waves are stabilized, and water flow is guided to enter the discharge culvert smoothly, the second stilling basin is designed as a down-dig type, the length L of the second stilling basin k = (0.7~0.8) L j , L j is the length of a free water jump, the height c of the tailgate of the second stilling basin h c -H1, h c " is the water depth after the jump, and H1 is the water depth on the top of the tailgate.

2. A hydraulic design method of guiding and energy dissipating for a double-curved spillway according to claim 1, characterized in that, The step (5) can keep the flow state of the stepped flow energy dissipation to ensure high energy dissipation rate, and control d c h / l < 0.0916 -1.276 , d c is the critical water depth, h is the step height, and l is the step length.

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