A design method for aeration erosion reduction facilities on the overflow surface of a steep slope spillway

Abstract

The present invention discloses a design method for aeration cavitation reduction facilities on the overflow surface of a steep spillway, which belongs to the technical field of water conservancy engineering. By analyzing local meteorological parameters, spillway body parameters and anti-cavitation working conditions, the cavitation risk is quickly evaluated and the layout position and parameters of the aeration cavitation reduction facilities are determined. The design process includes predicting the impact point position of the jet water tongue, the design of the sill and the drop sill, the parameter calculation of the vent pipe, and the evaluation of the aeration concentration along the overflow surface. This method can accurately design aeration cavitation reduction facilities, significantly improve the scientificity and efficiency of the spillway anti-cavitation design, effectively reduce the risk of cavitation damage, and provide a reliable design basis for water conservancy projects.

Description

Technical Field

[0001] The invention belongs to the technical field of water conservancy engineering, and in particular relates to a design method for an aeration erosion reduction facility on an overflow surface of a steep slope spillway. Background Art

[0002] Steep slope spillway is a commonly used flood discharge facility in water conservancy high dam hub projects. Due to the high head and high flow rate, its overflow surface often faces a high risk of cavitation. Therefore, in hydraulic design, it is crucial to quickly assess the cavitation risk of the overflow surface and take appropriate anti-cavitation measures. The inventor has proposed a method for assessing the cavitation risk of the overflow surface of a steep slope spillway in a public patent (CN118194421A). If the assessment results show that there is a risk of cavitation on the overflow surface, anti-cavitation measures must be taken in areas prone to cavitation.

[0003] Commonly used overflow surface anti-cavitation measures include reasonable body design, the use of materials with excellent impact resistance, control of the flatness of the overflow surface, and the installation of aeration cavitation reduction facilities. Although the first three measures can prevent cavitation damage to a certain extent, it is still difficult to completely eliminate the cavitation problem on steep slope spillways with high flow rates. In addition, these measures have high requirements on surface accuracy, are difficult to construct, and increase the cost. In contrast, the installation of aeration cavitation reduction facilities on steep slope overflow surfaces has been widely recognized as an economical and effective engineering measure to reduce or avoid cavitation damage caused by high-speed water flow through forced aeration.

[0004] Overflow surface aeration erosion reduction facilities are an engineering measure used to reduce the erosion and damage of water flow to overflow dams or hydraulic structures. Its working principle is to reduce the erosion of water flow and the impact and wear of water flow by mixing air when water flows through the overflow surface. This facility usually includes an air introduction device, which introduces air into the high-speed water flow through a guide groove or a special air inlet hole to form a bubble layer, reduce the direct contact between the water flow and the surface of the structure, and effectively extend the service life of the overflow dam and improve safety.

[0005] At present, there are many deficiencies and defects in the body design and aeration characteristics prediction methods of aeration cavitation reduction facilities on steep overflow surfaces, which are specifically manifested in the following aspects: First, the body design and aeration characteristics prediction of aeration cavitation reduction facilities in the design process mainly rely on engineering experience or qualitative estimation, and lack of systematic and scientific design standards and guidance. This practice of relying on experience often leads to the arbitrariness and uncertainty of the design scheme, and cannot guarantee the stability and effectiveness of the facilities under various working conditions. Secondly, the existing aeration characteristics prediction and estimation methods have large discreteness, and the prediction results obtained by different methods may be significantly different, making it difficult to form a unified design specification. This discreteness makes it difficult for designers to accurately predict the aeration effect in actual engineering applications, thereby affecting the cavitation reduction effect of the facility. In addition, due to the unknown scale effect, the traditional gravity similarity model test has obvious limitations in simulating and predicting the aeration situation of the prototype facility. The scale effect will cause errors between the model test and the actual working conditions, so that the test results cannot fully represent the actual aeration situation, which in turn affects the reliability of the design. At the same time, similar to the determination of the incipient cavitation number, the design of aeration cavitation reduction facilities often requires a decompression test. However, the implementation cost of the decompression test is high and the operation is complicated. In addition, the applicability and representativeness of the test results are also limited, which cannot meet the needs of fast and effective engineering design.

[0006] In summary, in order to improve the efficiency of anti-cavitation design of steep slope spillways, it is urgent to construct a convenient, fast and practical design method for aeration erosion reduction facilities on the overflow surface of steep slope spillways, so as to quickly provide decision support for the anti-cavitation design of spillways. Summary of the invention

[0007] In view of the problems existing in the prior art, the present invention provides a method for designing an aeration cavitation reduction facility on the overflow surface of a steep slope spillway, which solves the technical problems in the design process of aeration cavitation reduction facilities, such as the lack of systematic guidance for body design, large discreteness of aeration characteristic prediction methods, limitations of traditional model tests due to scale effects, complex decompression tests and lack of convenient design methods.

[0008] The present invention is implemented as follows: a design method for aeration erosion reduction facility on the overflow surface of a steep slope spillway, characterized by comprising the following steps:

[0009] S1. Determine the local meteorological parameters, spillway shape parameters and cavitation control conditions:

[0010] The local meteorological parameters include the local annual average temperature and average altitude; the spillway shape parameters include the number of spillway openings , Single hole discharge width 、Chute slope angle ; The anti-cavitation control conditions include the design flood level , Design flood flow ;

[0011] S2. Determine the location of the spillway surface on the steep slope where anti-cavitation measures are required based on the risk of cavitation on the spillway surface;

[0012] S3. Determine the location of the aeration cavitation reduction facility:

[0013] Determine the furthest possible location of the aeration cavitation reduction facility based on the layout of the gate piers between the overflow holes and the requirements for the layout of the vent pipes, compare the furthest possible location with the location where the anti-cavitation measures need to be adopted on the overflow surface of the steep slope spillway, and select the location closer to the upstream of the two locations as the location for the aeration cavitation reduction facility;

[0014] S4. Estimate the impact point of the jet water tongue behind the aeration cavitation reduction facility:

[0015] The length of the rear jet cavity of the aeration cavitation reduction facility is selected as four times the water depth of the location of the aeration cavitation reduction facility, and the location of the impact point of the rear jet water tongue of the aeration cavitation reduction facility is estimated according to the following formula:

[0016] (1)

[0017] (2)

[0018] (3)

[0019] in, is the jet cavity length, , are the horizontal distance and vertical distance from the location of the aeration cavitation reduction facility to the jet impact point, respectively. The water depth of the section where the aeration cavitation reduction facility is located;

[0020] S5. Design parameters for aeration cavitation reduction facilities:

[0021] The sill parameters include the sill angle and the sill height, which are calculated according to the following formula:

[0022] (4)

[0023] (5)

[0024] (6)

[0025] in, To pick corners and corners, To determine the height of the ridge, is the angle between the ridge surface and the horizontal direction, is the average flow velocity of the cross section at the location of the aeration cavitation reduction facility, , is the overflow surface single width flow, , is the acceleration due to gravity;

[0026] S6. Design parameters of the vent pipe of the aeration cavitation reduction facility:

[0027] The parameters of the ventilation pipe of the aeration cavitation reduction facility are the cross-sectional area of ​​the ventilation pipe: the maximum wind speed of the ventilation pipe is 62m / s, and the single-width ventilation volume of the overflow surface and the cross-sectional area of ​​the ventilation pipe are calculated according to the following formula:

[0028] (7)

[0029] (8)

[0030] (9)

[0031] in, is the ventilation volume per overflow surface width, is the cross-sectional area of ​​the ventilation pipe, is the average flow velocity of the cross section at the jet impact point, , are the horizontal distance and vertical distance from the location of the aeration cavitation reduction facility to the impact point of the jet water tongue centerline, respectively. , , is the correction value of the jet exit angle, , is the transverse pulsating velocity at the location of the aeration cavitation reduction facility, , is the overflow surface resistance coefficient, is the hydraulic radius of the section where the aeration cavitation reduction facility is located, is the air density, is the energy loss coefficient of the ventilation pipe, which is taken as 1.5. is the total ventilation volume of the overflow surface, , is the local atmospheric pressure;

[0032] S7. Design of drop parameters for aeration cavitation reduction facilities:

[0033] The drop parameter is the drop height. , It is the diameter of the ventilation pipe when its cross-sectional area is equivalent to a circle; , is the height of the vent outlet; the height of the drop is , The maximum value in ;

[0034] S8. Calculate the lower edge curve of the jet water tongue behind the aeration cavitation reduction facility:

[0035] Taking the vertex of the pick as the coordinate origin, numerically solve the following two equations:

[0036] (10)

[0037] (11)

[0038] in, For time, is the pressure factor, take 0.504, ; and The water jet motion equations respectively represent the horizontal and vertical displacements of the jet water tongue, describing the motion trajectory of the jet water tongue at the top of the sill.

[0039] Draw the lower edge curve of the jet water tongue along the overflow surface to determine the actual position coordinates of the jet water tongue impact point ( , ) and the position coordinates of the impact point of the jet water tongue centerline ( , ), and measure the actual jet cavity length ;

[0040] S9. Calculate the actual ventilator velocity and actual cavity pressure:

[0041] According to the actual jet trajectory, the average flow velocity of the jet impact point section is recalculated using formulas (7) and (8): And overflow surface single width ventilation , the actual ventilation pipe wind speed and actual cavity pressure are calculated using the following formula:

[0042] (12)

[0043] (13)

[0044] in, It represents the actual cross-sectional area of ​​the vent pipe;

[0045] S10. Calculate the average aeration concentration along the overflow surface section:

[0046] (14)

[0047] (15)

[0048] in, is the average air entrainment concentration in the cross section, is the aeration concentration at the jet impact point, , is the average aeration concentration of the section with sufficient aeration, is the oblique distance from the aeration cavitation reduction facility, is the velocity distribution unevenness coefficient of the section where the aeration cavitation reduction facility is located, which is taken as 1.05;

[0049] S11. Draw the distribution curve of aeration concentration along the overflow surface. If the end of the overflow surface is reached, ≥3%, the designed aeration cavitation reduction facility can effectively avoid cavitation damage on the overflow surface, and setting up one aeration cavitation reduction facility can meet the aeration requirements; if If the cavitation reduction rate is less than 3%, another aeration cavitation reduction facility should be installed. =3% is used as the location for arranging another aeration cavitation reduction facility, and steps S4 to S10 are repeated until the aeration concentration at the end of the overflow surface is ≥3%.

[0050] The design method of aeration erosion reduction facility for the overflow surface of the steep slope spillway has many advantages and significant effects:

[0051] First, based on the cavitation risk assessment of the overflow surface of the steep spillway, this method can quickly identify and quantify potential cavitation risks to ensure the scientificity and reliability of the design. By combining the meteorological parameters of the project site, the design size parameters of the spillway, and the flow parameters under the design conditions, this method can quickly assess the cavitation risk of the overflow surface, making the design process more efficient and convenient.

[0052] Secondly, the method can accurately determine the size of the aeration cavitation reduction facility, thereby optimizing the design and improving the cavitation reduction effect of the facility. This accuracy not only reduces the trial and error cost in the design, but also greatly improves the spillway's anti-cavitation performance and extends the service life of the facility.

[0053] In addition, the method also has the function of predicting aeration characteristics, allowing designers to predict the aeration effect at an early stage, reduce uncertainty, and ensure the successful implementation of the design. This prediction capability provides a more comprehensive and scientific design basis for water conservancy projects, helping to improve the safety and stability of the entire project.

[0054] Overall, this design method significantly improves the efficiency and scientificity of spillway anti-cavitation design, provides a set of simple, effective and reliable design tools for water conservancy projects, and helps promote the development and application of related technologies. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 It is a schematic diagram of the layout of typical aeration cavitation reduction facilities and their water flow patterns;

[0056] Figure 2 is a longitudinal centerline cross-section of the spillway in a specific embodiment;

[0057] Figure 3 is a schematic diagram of the arrangement position of the aeration cavitation reduction facility in a specific embodiment;

[0058] Figure 4 is a design layout diagram of the aeration cavitation reduction facility in a specific embodiment;

[0059] Figure 5 is a curve distribution diagram of the lower edge of the jet water tongue in a specific embodiment;

[0060] Figure 6 is a distribution diagram of average aeration concentration along the cross section of the overflow surface in a specific embodiment;

[0061] Figure 7 It is a flow chart of the anti-cavitation design method. DETAILED DESCRIPTION

[0062] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0063] In order to solve the technical problems such as lack of systematic guidance on body design, large discreteness of aeration characteristic prediction method, limitation of traditional model test by scale effect, complex decompression test and lack of convenient design method in the design process of aeration cavitation reduction facilities, the present invention provides a design method for aeration cavitation reduction facilities on the overflow surface of a steep slope spillway. In order to further illustrate the structure of the present invention, the detailed description is as follows in conjunction with the attached drawings:

[0064] In the overflow surface aeration cavitation reduction facility, the aeration cavitation reduction facility reduces the cavitation effect of the water flow by introducing air into the high-speed water flow, thereby protecting the overflow surface from erosion. The sill and the drop sill are commonly used aeration facilities. The former creates a drop in height on the overflow surface, and the latter gradually reduces the energy of the water flow through a stepped structure, so that the water flow forms a vortex area behind these structures, and the air is drawn into the water flow to achieve an aeration effect. The vent pipe serves as an auxiliary facility to introduce atmospheric air into the water flow to enhance the aeration effect. These structures cooperate with each other to form an effective aeration cavitation reduction system. The present invention proposes a design method for an aeration cavitation reduction facility for the overflow surface of a steep slope spillway, such as Figure 7 , including the following steps:

[0065] S1. Determine the local meteorological parameters, spillway shape parameters and cavitation control conditions:

[0066] The local meteorological parameters include the local annual average temperature and average altitude; the spillway shape parameters include the number of spillway openings , Single hole discharge width 、Chute slope angle ; The anti-cavitation control conditions include the design flood level , Design flood flow ;

[0067] S2. Determine the location where anti-cavitation measures are required on the overflow surface of the steep spillway according to the cavitation risk of the overflow surface. In this embodiment, the technical solution described in the published patent application (CN118194421A, a method for assessing the cavitation risk of the overflow surface of a steep spillway) is used to obtain the location where anti-cavitation measures are required.

[0068] S3. Determine the location of the aeration cavitation reduction facility:

[0069] The farthest possible location of the aeration cavitation reduction facility is determined based on the layout of the gate piers between the overflow holes and the requirements for the layout of the vent pipes. The farthest possible location is compared with the location where anti-cavitation measures are required on the overflow surface of the steep slope spillway, and the location closer to the upstream of the two locations is selected as the location for the aeration cavitation reduction facility. When determining the location of the aeration cavitation reduction facility, it is necessary to comprehensively consider the layout of the gate piers between the overflow holes and the installation requirements of the vent pipes. Since the vent pipes on both sides of the aeration cavitation reduction facility need to be installed in the gate piers, the farthest location of the facility should be based on the layout of the gate piers. On this basis, combined with the area that needs to be treated with anti-cavitation, the aeration cavitation reduction facility is finally arranged on the side closer to the upstream of the above two locations.

[0070] Typical aeration cavitation reduction facility layout and water flow patterns are as follows: Figure 1 As shown in the figure, the commonly used aeration cavitation reduction facilities on steep slopes include the sill and the drop sill. The sill can eject the water flow upward and form a cavity under the sill to aerate the water flow. The drop sill can effectively increase the length of the jet cavity without affecting the flow state of the water flow. The combination of the sill and the drop sill can achieve a better cavitation reduction effect. The vent pipe connects the atmosphere and the cavity behind the sill and is a device for supplying air to the cavity. In order to ensure smooth and reliable air intake, the vent pipe system can be buried in the gate walls on both sides.

[0071] S4. Estimate the impact point of the jet water tongue behind the aeration cavitation reduction facility:

[0072] The length of the rear jet cavity of the aeration cavitation reduction facility is selected as four times the water depth of the location of the aeration cavitation reduction facility, and the location of the impact point of the rear jet water tongue of the aeration cavitation reduction facility is estimated according to the following formula:

[0073] (1)

[0074] (2)

[0075] (3)

[0076] in, is the jet cavity length, , are the horizontal distance and vertical distance from the location of the aeration cavitation reduction facility to the jet impact point, respectively. It is the cross-sectional water depth at the location of the aeration cavitation reduction facility, which is obtained by interpolating the water surface line along the route calculated by the published patent (CN118194421A, a method for assessing cavitation risk of the overflow surface of a steep spillway). The following overflow surface depth parameters along the route are obtained by this method. Existing studies have shown that the cavity length should be greater than 3 to 5 times the water depth at the location of the aeration cavitation reduction facility. Combined with engineering practice experience, the cavity length is selected as four times the water depth at the location of the aeration cavitation reduction facility, taking into account the anti-cavitation effect and the influence of the aeration cavitation reduction facility on the flow state.

[0077] S5. Design parameters for aeration cavitation reduction facilities:

[0078] The sill parameters include the sill angle and the sill height, which are calculated according to the following formula:

[0079] (4)

[0080] (5)

[0081] (6)

[0082] in, To pick corners and corners, To determine the height of the ridge, is the angle between the ridge surface and the horizontal direction, is the average flow velocity of the cross section at the location of the aeration cavitation reduction facility, , is the overflow surface single width flow, , is the acceleration due to gravity;

[0083] S6. Design parameters of the vent pipe of the aeration cavitation reduction facility:

[0084] The parameters of the ventilation pipe of the aeration cavitation reduction facility are the cross-sectional area of ​​the ventilation pipe: the maximum wind speed of the ventilation pipe is 62m / s, and the single-width ventilation volume of the overflow surface and the cross-sectional area of ​​the ventilation pipe are calculated according to the following formula:

[0085] (7)

[0086] (8)

[0087] (9);

[0088] in, is the ventilation volume per overflow surface width, is the cross-sectional area of ​​the ventilation pipe, is the average flow velocity of the cross section at the jet impact point, , are the horizontal distance and vertical distance from the location of the aeration cavitation reduction facility to the impact point of the jet water tongue centerline, respectively. , , is the correction value of the jet exit angle, , is the transverse pulsating velocity at the location of the aeration cavitation reduction facility, , is the overflow surface resistance coefficient, is the hydraulic radius of the section where the aeration cavitation reduction facility is located, is the air density, is the energy loss coefficient of the ventilation pipe, which is taken as 1.5. is the total ventilation volume of the overflow surface, , is the local atmospheric pressure.

[0089] According to relevant engineering practice experience, in order to avoid excessive noise and airflow instability in the ventilation duct, the ventilation duct wind speed should not be too high. Based on domestic and foreign design experience, the ventilation duct design wind speed is 62m / s.

[0090] The cross-section of the vent pipe is designed to be rectangular. The cross-section area of ​​the vent pipe and the layout of the gate pier structure are comprehensively calculated to determine the length, width and vertical height of the vent pipe. In order to ensure the convenience of construction and the safety of aeration, the plane size of the vent pipe can be rounded up as much as possible. The actual cross-section area of ​​the vent pipe It may be slightly larger than the calculated value.

[0091] S7. Design of drop parameters for aeration cavitation reduction facilities:

[0092] The drop parameter is the drop height. , It is the diameter of the ventilation pipe when its cross-sectional area is equivalent to a circle; , is the height of the vent outlet; the height of the drop is , The maximum value in .

[0093] In this embodiment, the height of the drop is ,in d e is the redundancy. When designing steep slopes and drops, the layout of the vent pipe outlets should be considered. The vent pipe outlets should all be located inside the cavity, and a certain redundancy should be left.

[0094] S8. Calculate the lower edge curve of the jet water tongue behind the aeration cavitation reduction facility:

[0095] Taking the vertex of the pick as the coordinate origin, numerically solve the following two equations:

[0096] (10)

[0097] (11)

[0098] in, For time, is the pressure factor, take 0.504, ; and The water jet motion equation represents the displacement of the jet water tongue in the horizontal and vertical directions respectively, and describes the motion trajectory of the jet water tongue at the top of the sill.

[0099] Draw the lower edge curve of the jet water tongue along the overflow surface to determine the actual position coordinates of the jet water tongue impact point ( , ) and the position coordinates of the impact point of the jet water tongue centerline ( , ), and measure the actual jet cavity length .

[0100] S9. Calculate the actual ventilator velocity and actual cavity pressure:

[0101] According to the actual jet trajectory, the average flow velocity of the jet impact point section is recalculated using formulas (7) and (8): And overflow surface single width ventilation , the actual ventilation pipe wind speed and actual cavity pressure are calculated using the following formula:

[0102] (12)

[0103] (13)

[0104] in, It represents the actual cross-sectional area of ​​the ventilation pipe.

[0105] S10. Calculate the average aeration concentration along the overflow surface section:

[0106] (14)

[0107] (15)

[0108] in, is the average air entrainment concentration in the cross section, is the aeration concentration at the jet impact point, , is the average aeration concentration of the section with sufficient aeration, is the oblique distance from the aeration cavitation reduction facility, is the velocity distribution unevenness coefficient of the section where the aeration cavitation reduction facility is located, and is taken as 1.05.

[0109] S11. Draw the distribution curve of aeration concentration along the overflow surface. If the end of the overflow surface is reached, ≥3%, the designed aeration cavitation reduction facility can effectively avoid cavitation damage on the overflow surface, and setting up one aeration cavitation reduction facility can meet the aeration requirements; if If the cavitation reduction rate is less than 3%, another aeration cavitation reduction facility should be installed. =3% is used as the location for arranging another aeration cavitation reduction facility, and steps S4 to S10 are repeated until the aeration concentration at the end of the overflow surface is ≥3%.

[0110] According to relevant engineering practice experience, within the protection range of the aeration cavitation reduction facilities, the aeration concentration near the wall shall not be less than 3%, and the aeration concentration on the wall to avoid cavitation shall be considered as 3%. Specific embodiment:

[0112] A high dam spillway project is located in an area with an annual average temperature of 22°C and an average altitude of 1200m. The spillway is designed with 5 holes, with orifice dimensions of 12.40m×17.50m (width×height), and the weir top elevation is 612.50m. The weir surface adopts the WES curve, and the slope ratio of the downstream slope section of the weir top is 0.8:1. The longitudinal centerline section of the spillway is arranged as follows: Figure 2 The reservoir design flood level is 630.00m, and the design flood flow is 9884m3 / s.

[0113] The slope angle of the spillway in the slope section reaches 51.34°, which is a typical steep slope spillway.

[0114] First, the cavitation risk of the overflow surface of the steep slope spillway in the specific embodiment is evaluated:

[0115] S1. According to the meteorological data of the project site, the local annual average temperature is 22℃ and the average altitude is 1200m. According to formulas (1), (2) and (3), the local water density can be calculated to be 997.8462m3 / s, the vapor pressure is 2.6648kPa and the atmospheric pressure is 89.0859kPa respectively.

[0116] S2. According to the engineering design data, the spillway body parameters are as follows: the number of orifices is 5, the single-hole discharge width is 12.40m, and the chute slope angle is 51.34°; the cavitation risk control conditions are as follows: the design flood level is 630.00m, and the design flood flow is 9884m3 / s.

[0117] S3. The top of the overflow weir is taken as the initial section for calculation. The water level at the top of the weir is equal to the design flood level of the reservoir. The water surface line along the spillway is preliminarily calculated using the segmented trial algorithm.

[0118] S3.1. Taking the weir top as section I, the overflow surface is divided into 13 sections, with a total of 14 characteristic sections. The overflow surface sections and characteristic section positions are as follows: Figure 3 , the characteristic section related parameters are listed as follows Figure 4 .

[0119] S3.2. Calculate the hydraulic parameters of control section I, which are: water depth =17.5m, flow area =217m2, average flow rate =9.1097m / s, wet perimeter =47.4m, hydraulic radius =4.5781m.

[0120] S3.3, set iteration conditions, water level increment =0.0001m, allowable error =1%.

[0121] S3.4-S3.6, use the trial method to calculate the water depth of section II and other sections according to formulas (4), (5), (6), and (7). Draw the water surface elevation change curve along the route ~ ,like Figure 5 shown.

[0122] S4. Calculate the average flow velocity and cavitation number of the cross section according to formulas (8), (9), and (10), and draw the flow velocity change curve along the process. ~ And the cavitation number change curve of the water flow along the way ~ ,like Figure 6 shown.

[0123] S5. According to Figure 6 Distribution shows that there is a large area on the overflow surface where the average cross-sectional flow velocity is greater than 30 m / s and the water cavitation number is less than 0.2. According to the comprehensive judgment standard for the cavitation risk of the overflow surface, there is a cavitation risk on the overflow surface.

[0124] S6. Determine the areas where anti-cavitation measures are required:

[0125] Step 1: Critical flow rate =30m / s, primary cavitation number = 0.2 horizontal distance from the weir top =34.40m, =42.31m, the horizontal distance from the weir top to the part where anti-cavitation measures are required =34.40m.

[0126] Step 2: Find the position on the overflow surface that is 34.40m horizontally away from the weir crest. The cross-sectional elevation at this position is =581.48m.

[0127] Based on the risk assessment results, the aeration erosion reduction facilities on the overflow surface of the steep slope spillway are designed:

[0128] S1. According to the engineering design data, the local annual average temperature is 22℃ and the average altitude is 1200m; the number of spillway openings is 5, the single-hole discharge width is 12.4m, and the chute slope angle is 51.34°; the design flood level is 630.00m and the design flood flow is 9884 m3 / s.

[0129] S2. The above risk assessment method is used to calculate the local water density of 997.7644m3 / s, the vapor pressure of 2.662kPa, and the atmospheric pressure of 86.4549kPa. According to the calculation results of the hydraulic parameters along the overflow surface, there is a large area on the overflow surface where the average flow velocity of the section is greater than 30m / s and the cavitation number of the water flow is less than 0.2. There is a cavitation risk on the overflow surface, and the horizontal distance from the part where anti-cavitation measures are required to be taken is 34.40m from the weir top.

[0130] S3. To ensure the air supply effect of the vent pipe into the cavity, the cross-section of the vent pipe can be larger along the cavity direction. Combined with the layout of the gate piers between the overflow holes, the vent pipe inlet is set on the last gate pier, and the cross-section length of the vent pipe is set to 4m. In order to leave a certain safety thickness between the inner wall of the vent pipe and the side wall of the gate pier, the vent pipe is arranged vertically along the height direction and two bends are set. The safety thickness between the inner wall of the vent pipe and the side wall of the gate pier is 2m, so the farthest possible location for the aeration cavitation reduction facility is set at a horizontal distance of 6m above the end of the gate pier. Figure 3 As shown, this position is closer to the upstream than the position determined in the above steps, so it is used as the location for arranging the aeration cavitation reduction facility.

[0131] S4. The water depth of the interpolated aeration cavitation reduction facility location is 5.42m, the estimated jet cavity length is 21.68m, the horizontal distance from the jet impact point to the aeration cavitation reduction facility location is 13.54m, and the vertical distance is 16.93m.

[0132] S5. The angle of the cantilever is calculated to be 4.06°, and the height of the cantilever is calculated to be 0.22m.

[0133] S6. The ventilation volume per overflow surface is calculated to be 16.81m3 / s·m, and the cross-sectional area of ​​the ventilation pipes on both sides is calculated to be 3.68m2. The ventilation pipe is designed to be a rectangular cross-section with a cross-sectional length of 4m. The cross-sectional width is calculated to be 0.46m. Rounding up, the cross-sectional width is set to 0.5m, and the actual cross-sectional area of ​​the ventilation pipes on both sides is 4 m2.

[0134] S7. The diameter of the ventilation pipe when the cross-sectional area is equivalent to a circle is 1.60m. The difference between the ventilation pipe outlet height and the height of the sill is 0.28m. Considering the 7cm redundancy, the height of the sill is designed to be 0.35m. Figure 4 .

[0135] S8, the lower edge curve of the jet water tongue is shown Figure 5 The actual jet water tongue impact point coordinates are (15.50m, 20.29m), the jet water tongue centerline impact point coordinates are (17.50m, 22.13m), and the actual jet cavity length is measured to be 25.56m. The cavity length considering only the ridge is 21.67m, which is basically consistent with the initial estimate.

[0136] S9, recalculate the average flow velocity of the jet impact point section to be 36.54m / s, and the single-width ventilation volume of the overflow surface under the combination of the ridge and the drop is 19.32 m 3 / s·m. The actual ventilation pipe wind speed is 59.90m / s and the actual cavity pressure is 81.03kPa

[0137] S10, the aeration concentration at the starting position of the jet impact point is 10.81%, the average aeration concentration of the section with sufficient aeration is 0.62%, and the average aeration concentration distribution along the overflow surface is shown in Figure 6 The average aeration concentration at the end section of the overflow surface is 4.6%. The designed aeration cavitation reduction facility can effectively avoid cavitation damage on the overflow surface. Setting up one aeration cavitation reduction facility can meet the aeration requirements.

[0138] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A design method for aeration erosion reduction facilities on the overflow surface of a steep slope spillway, characterized in that The following steps are involved: S1. Determine the local meteorological parameters, spillway shape parameters and cavitation control conditions: The local meteorological parameters include the local annual average temperature and average altitude; the spillway shape parameters include the number of spillway openings , Single hole discharge width 、Chute slope angle ; The anti-cavitation control conditions include the design flood level , Design flood flow ; S2. Determine the location of the spillway surface on the steep slope where anti-cavitation measures are required based on the risk of cavitation on the spillway surface; S3. Determine the location of the aeration cavitation reduction facility: Determine the furthest possible location of the aeration cavitation reduction facility based on the layout of the gate piers between the overflow holes and the requirements for the layout of the vent pipes, compare the furthest possible location with the location where the anti-cavitation measures need to be adopted on the overflow surface of the steep slope spillway, and select the location closer to the upstream of the two locations as the location for the aeration cavitation reduction facility; S4. Estimate the impact point of the jet water tongue behind the aeration cavitation reduction facility: The length of the rear jet cavity of the aeration cavitation reduction facility is selected as four times the water depth of the location of the aeration cavitation reduction facility, and the location of the impact point of the rear jet water tongue of the aeration cavitation reduction facility is estimated according to the following formula: （1） （2） （3） in, is the jet cavity length, , are the horizontal distance and vertical distance from the location of the aeration cavitation reduction facility to the jet impact point, respectively. The water depth of the section where the aeration cavitation reduction facility is located; S5. Design parameters for aeration cavitation reduction facilities: The sill parameters include the sill angle and the sill height, which are calculated according to the following formula: （4） （5） （6） in, To pick corners and corners, To determine the height of the ridge, is the angle between the ridge surface and the horizontal direction, is the average flow velocity of the cross section at the location of the aeration cavitation reduction facility, , is the overflow surface single width flow, , is the acceleration due to gravity; S6. Design parameters of the vent pipe of the aeration cavitation reduction facility: The parameters of the ventilation pipe of the aeration cavitation reduction facility are the cross-sectional area of ​​the ventilation pipe: the maximum wind speed of the ventilation pipe is 62m / s, and the single-width ventilation volume of the overflow surface and the cross-sectional area of ​​the ventilation pipe are calculated according to the following formula: （7） （8） （9） in, is the ventilation volume per overflow surface width, is the cross-sectional area of ​​the ventilation pipe, is the average flow velocity of the cross section at the jet impact point, , are the horizontal distance and vertical distance from the location of the aeration cavitation reduction facility to the impact point of the jet water tongue centerline, respectively. , , is the correction value of the jet exit angle, , is the transverse pulsating velocity at the location of the aeration cavitation reduction facility, , is the overflow surface resistance coefficient, is the hydraulic radius of the cross section of the aeration cavitation reduction facility, is the air density, is the energy loss coefficient of the ventilation pipe, which is taken as 1.

5. is the total ventilation volume of the overflow surface, , is the local atmospheric pressure; S7. Design of drop parameters for aeration cavitation reduction facilities: The drop parameter is the drop height. , It is the diameter of the ventilation pipe when its cross-sectional area is equivalent to a circle; , is the height of the vent outlet; the height of the drop is , The maximum value in ; S8. Calculate the lower edge curve of the jet water tongue behind the aeration cavitation reduction facility: Taking the vertex of the pick as the coordinate origin, numerically solve the following two equations: （10） （11） in, For time, is the pressure factor, take 0.504, ; and The water jet motion equations respectively represent the horizontal and vertical displacements of the jet water tongue, describing the motion trajectory of the jet water tongue at the top of the sill. Draw the lower edge curve of the jet water tongue along the overflow surface to determine the actual position coordinates of the jet water tongue impact point ( , ) and the position coordinates of the impact point of the jet water tongue centerline ( , ), and measure the actual jet cavity length ; S9. Calculate the actual ventilator velocity and actual cavity pressure: According to the actual jet trajectory, the average flow velocity of the jet impact point section is recalculated using formulas (7) and (8): And overflow surface single width ventilation , the actual ventilation pipe wind speed and actual cavity pressure are calculated using the following formula: （12） （13） in, It represents the actual cross-sectional area of ​​the vent pipe; S10. Calculate the average aeration concentration along the overflow surface section: （14） （15） in, is the average air entrainment concentration in the cross section, is the aeration concentration at the jet impact point, , is the average aeration concentration of the section with sufficient aeration, is the oblique distance from the aeration cavitation reduction facility, is the velocity distribution unevenness coefficient of the section where the aeration cavitation reduction facility is located, which is taken as 1.05; S11. Draw the distribution curve of aeration concentration along the overflow surface. If the end of the overflow surface is reached, ≥3%, the designed aeration cavitation reduction facility can effectively avoid cavitation damage on the overflow surface, and setting up one aeration cavitation reduction facility can meet the aeration requirements; if If the cavitation reduction rate is less than 3%, another aeration cavitation reduction facility should be installed. =3% is used as the location for arranging another aeration cavitation reduction facility, and steps S4 to S10 are repeated until the aeration concentration at the end of the overflow surface is ≥3%.

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