Influence Of Pier Layout On Hydraulic Characteristics Of Bend Flow

With the continuous development and construction of river related Bridge Engineering in China,bridge engineering has gradually become an important carrier of personnel,material and cultural exchanges between the two sides of the river.The infrastructure construction of river bridge is bound to have many adverse effects on the resistance of riverbed near the bridge,river regime,flood carrying capacity and bank stability.Therefore,it is of positive significance to predict and calculate the backwater law and flow field structure near the bridge pier,and evaluate the change trend of river regime after the bridge construction.This paper first analyzed and summarized the previous research results on upstream backwater and downstream river regime of river related bridges.On this basis,based on the physical model test,the influence of river related bridges on flow hydraulic characteristics in curved river was studied.Analysis of the corresponding hydraulic parameters and variation,numerical simulation for related problems.The main research contents and conclusions are as follows:(1)A physical model was established to research the characteristics of backwater level and velocity variation near the pier in curved river.Based on the test results,the local head loss coefficient of the pier was calculated.The drag coefficient was calculated by momentum equation,continuity equation and boundary layer theory.According to the hydraulic parameters obtained from the test and calculation,through the derivation of the hydraulic formula,the Yarnell formula,which is widely used at present,was improved,and a new calculation method for calculating the maximum backwater level in the upstream of the bridge was obtained.(2)The numerical simulation was carried out on the basis of the experiment by using FLUENT software.According to the numerical simulation results,the newly introduced parameters in the improved Yarnell formula was calibrated,and the maximum backwater level of the bridge upstream calculated by the improved formula was in good agreement with the experimental results.The structure of flow field around the piers is analyzed.The results show that the orthogonal arrangement of piers makes the flow velocity distribution in the bend uniform.At the same time,the flow field around the piers is quite different in different water depths under the coupling effect of the flow around the piers and the circulation in the bend.(3)The backwater height of the upstream pier decreases with the increase of the skew angle of the bridge and river when the bridge and river cross obliquely.According to the test and simulation results,the linear relationship between the reduction factor of backwater height and the skew angle was fitted.According to the statistics of left and right bank water level,downstream flow velocity of bridge pier and deflection angle of water flow under bridge under different skew angles,the deflection degree of bridge pier to water flow was quantified,and the skew angle of bridge and river between 20° and 25° is the most unfavorable condition.