Experimental Study On Optimization Of Aerated Tanks For Combined Energy Dissipators

China's first joint energy dissipation method combining wide-tailed pier + stepped overflow dam + stilling pool is widely used in large and medium-sized hydraulic flood discharge buildings because of its high energy dissipation effect and good economic benefits.With the development of China's high water head and large singlewide river channel in the western mountainous area,the energy dissipation mode of this new type of combined energy dissipa tor has problems such as dam body damage and dam foundation instability in the high dam drainage construction project.Especially in the actual project,it is found that when the stepped overflow dam vents high-speed water flow,cavitation cavitation damage is likely to occur at the exit of the exit of the step overflow dam,the concrete material on the surface of the dam is severely peeled off.Therefore,domestic and foreign water conservancy workers have to solve the problem of water tongue instability and cavitation and erosion on the dam surface in the process of flood discharge operation,Therefore,in order to solve the problem of water tongue instability and cavitation and erosion on the dam surface during the flood discharge operation,water conservancy workers at home and abroad often set aeration tanks at the junction of the WES curve and the step overflow dam.The aeration of the water body is enhanced by the forced aeration of the bottom to enhance the aeration of the dam surface.The predecessors' research on aeration is mainly carried out by numerical analysis of mathematical models or analysis of some hydraulic characteristics of bottom water head and small single flow.Based on the A hai Hydropower Station,three different angles and three different heights of aerated tanks were designed on the physical model of the overflow surface.Firstly,the influence of aeration angle or height on the hydraulic characteristics of the stepped cavity of the wide-tailed pier +stepped overflow dam + the stilling pool combined energy dissipation mode,the aeration concentration along the path,etc.,is analyzed by a single factor;Furthermore,the three aeration angles and the three aeration heights were combined and analyzed in nine groups to explore the main factors affecting the hydraulic characteristics such as erosion and energy dissipation of the stepped overflow dam.In order to improve the aerated tank type,the theoretical basis for the design of the combined energy dissipator of the stepped overflow dam under high head and large single flow is provided.The main research results are as follows:1? Compared with the aeration tank not installed,the addition of the aeration tank can significantly increase the length and area of the aeration cavity of the step surface,and the aeration concentration of the water flow also increases.Keeping the height of the aeration chamber constant,the cavity and aeration concentration of the step surface increase with the increase of the aeration angle,and the negative pressure on the step surface decreases.When the aeration angle is constant and the height of the ridge is increased from 0.7m to 1.3m,it is beneficial to increase the aeration cavity and area of the step surface,and increase the aeration concentration of the step surface,which can effectively avoid the cavitation damage of the step surface.2?Whether or not the aeration tank is added has little influence on the uniform pressure of the stepped overflow dam,the depth of the stilling pool and the variation of the flow velocity along the path.When the aeration angle is increased from 7° to 11.3° or the aeration height is increased from0.7m to 1.3m,the direct impact of the upstream water flow on the dam surface can be increased.The central axis of the step section model and the center of the overflow surface The time-averaged pressure on the line increases.Similarly,the water depth of the stilling pool is also significantly increased,and the flow velocity at the bottom is correspondingly reduced,and the energy dissipation effect is better as the angle and height of the aerator are increased.3?The sensitivity analysis of the aeration characteristics of the steppedoverflow dam by the combination of the aerated angle and the height of the aerated dam can be seen that the variance results show that increasing the aeration angle increases the aeration of the stepped overflow dam and reduces the negative pressure of the stepped surface.The impact is greater and is in a dominant position compared to the height of the ridge.The variance is consistent with the conclusion of the range analysis.4?According to the analysis of variance and variance,it is known that the ridge height has a greater effect on the upstream flow than the angle of the aerated ridge,so the height of the aeration has a significant influence on the average pressure of the reverse arc.The time-averaged pressure value of the stilling pool is the result of the interaction of the upstream water tongue impact and the aeration.The significant effect of the aerated angle and height on the minimum time-average pressure of the stilling pool is not much different.5?According to the variance and range analysis of the velocity of flow and energy dissipation rate of the stepped overflow dam,the aeration height is the main factor affecting the velocity of flow and energy dissipation rate of the stepped overflow dam.This shows that the height of the aeration tank increases,and the direct impact of the water flow on the dam surface is increased,and the large kinetic energy of the water body can be obviously weakened,which is beneficial to reduce the length of the work of the stilling pool.In summary.Under the condition of high head and large single flow,comprehensive consideration is given to the factors such as the fa?ade and horizontal plane erosion reduction effect of the stepped overflow dam combined with the energy dissipator,the scouring strength and energy dissipation rate of the upstream dam body.The shape of the aerator is 11.3°and the height of 1.0m is the best test solution.