Experimental Study On Hydraulic Characteristics Of Stilling Basin With Pile-like Tail Sill

The tail sill can change the position of hydraulic jump,shorten the length,and regulate the flow pattern in stilling basin.At present,there have been many studies on the shape of tail sills,such as rectangular,trapezoidal,triangular and other solid tail sills.Although the shape has a certain improvement on the energy dissipation efficiency,it cannot reduce the disadvantage of cavitation damage on the surface.At the same time,the solid tail sill will produce large water surface elevation,and the recirculation zone behind the sill also partially hinders water exchange and leads to poor water quality.Since the 18 th National Congress of the Communist Party of China(CPC),the state has clearly put forward“To integrate the concept of ecological civilization into all aspects of water conservancy planning,construction and management”,this study on the tail sill of stilling basin is the embodiment of implementing the concept of scientific development and promoting the construction of water ecological civilization.In this study,according to the small and medium-sized rivers with low Froude number in northern China,the solid tail sill was substituted by a multi-row scattered pile column(cross section is circular),and a new type of tail sill was proposed,namely the pile-like tail sill.When the pile raise the backwater,the turbulent characteristics of flow around the pile group are increased,and the energy dissipation effect is also increased.Pile-like tail sill can play the role of traditional tail sill on the basis of solving the problem of water convergence in and out of the stilling basin,which can improve the water ecological environment on the basis of realizing the function of traditional hydraulic structure.This study adopts the method of combining theoretical analysis,hydraulic model test and statistical analysis.By changing the parameters such as the height,diameter,spacing of the pile column,rows number and arrangement position of the pile column,22 different schemes(a total of 115 groups)were carried out and the corresponding physical model test of the pile column and the comparative test of the solid tail sill were established.The influence of the parameters of the pile-like tail sill on the hydraulic characteristics,hydraulic jump characteristics and energy dissipation effect of the stilling basin were studied by model test under different flow discharges.The main conclusions are as follows:(1)Based on the study of hydraulic characteristics along the pile-like tail sill in the stilling basin,it is found that the factors of pile heights,rows number and spacing have great influence on hydraulic characteristics.In the range of the test parameters,the higher pile,the more rows and the smaller spacing,the greater the backwater effect of the pile,the more difficult the hydraulic jump type is affected by the disacharge change,the smaller the water level difference,the more uniform the flow distribution.(2)Research on the hydraulic jump characteristics of the pile-like tail sill in the stilling basin,showed that the position of the initial section of the hydraulic jump moves backward with the increase of the flow rate,the hydraulic jump length decreases,the water depth and height after the hydraulic jump are increase.The factors of pile height,rows number,diameter and spacing have great influence on the hydraulic jump characteristics.With the increase of pile height,rows number and the decrease of diameter and spacing,the occurring position of hydraulic jump move forward,while length of hydraulic jump becomes longer,and the water depth and height after hydraulic jump decrease.The influence of arrangement position of the pile column on the hydraulic jump characteristics is relatively small.The closer the pile layout position,the longer the hydraulic jump length and the higher the hydraulic jump height and the water depth after the hydraulic jump are slightly reduced.(3)The study on the energy dissipation effect of pile-like tail sill in the stilling basin showed that the energy dissipation rate of stilling basin and pile-like area decrease with the increase of the discharge.The influence of height and spacing on the energy dissipation rate of stilling basin is consistent.When the flow discharge is small,the lower the pile height and the larger the spacing have the higher energy dissipation rates.With the increase of discharge,the energy dissipation of the stilling basin with higher pile and smaller spacing decreases at first and then increases.The more rows,the higher the energy dissipation rate of stilling basin and pile-like area;the energy dissipation rate of the stilling basin has little difference under different flow discharges when the piles are arranged in different positions.But when the pile-like tail sill is arranged forward,the energy dissipation rate of the pile-like area is obviously improved.(4)The conjugate water depth formula and hydraulic jump length formula of pile-like tail sill in the stilling basin were established by multiple regression method considering the parameters such as water depth before and after the hydraulic jump and the hydraulic jump length.The calculation formula of pile-like resistance is obtained by considering the coefficients of lateral and longitudinal resistance,which can be used as reference for engineering design.