Model Test And Numerical Simulation Of Transparent Debris Flow Impact On Bridge Pier Based On PIV Technology

Debris flow is a kind of geological disaster which is composed of water,sand,stone and so on.It has high velocity,high energy and strong destruction.When debris flow occurs in mountainous area,it will pose a serious threat to bridge structure,especially bridge pier.In this paper,two kinds of transparent debris flow bodies are configured by using transparent and viscous 550USP white oil,350USP white oil and 68#oil.PIV technology was used to carry out laboratory model test of transparent debris flow impacting bridge pier,and the flow field characteristics of debris flow impacting bridge pier with different section shapes under different slope and viscosity conditions were obtained,and the impact characteristics of debris flow were analyzed.The CFD numerical simulation of scale and full scale was carried out by Ansys Fluent,and the experimental results were extended to obtain the movement characteristics and dynamic characteristics of debris flow impacting bridge pier.The specific contents and conclusions are as follows:(1)Using 550USP white oil,350USP white oil and 68#oil to configure two kinds of transparent debris flow body and design a model test system of transparent debris flow impacting bridge pier based on PIV technology,to realize the observation and analysis of flow morphology and movement characteristics of debris flow,and record the impact force data of debris flow impacting bridge pier.In this paper,a total of 21 groups of tests were carried out to study the impact of transparent debris flow on round,square and round-end bridge piers.The relationship between debris flow height and surface velocity,the relationship between debris flow impact force and flow characteristics,the relationship between debris flow depth and surface velocity under stable flow state,and the distribution characteristics of debris flow velocity under stable flow state are obtained.(2)A scale CFD numerical model is established by using Ansys Fluent software.The bridge pier with circular,square and round-end impact sections of debris flow under the condition of lateral constraint is simulated.The impact force of debris flow on the bridge pier and the counter image of debris flow velocity are analyzed by changing the pier section shape and debris flow velocity.The empirical formula and the relation between the pier section shape,flow characteristic value of debris flow and flow velocity distribution,impact resistance coefficient C_d andC_d’under the condition of confining are obtained.(3)A full-size CFD numerical model based on the measured parameters of muddy ditch debris flow was established by Ansys Fluent to simulate the impact of debris flow on a single pier and a double circular pier under unconfined conditions.By changing the section shape,the aspect ratio of the round-end section,the flow velocity of debris flow,and the pier edge distance,counter of debris flow velocity,the debris flow on the impact of the bridge pier,the pier surface pressure distribution,the suitable conditions broader pier cross-section shape,pier spacing,rounded shape cross section aspect ratio,and the experience formula of debris flow Reynolds number Re,froude number Fr and debris flow impact pressure distribution impact the relationship between the resistance coefficient C_d andC_d’obtained.