Analysis Of Force And Flow Characteristics Of Flow Around Columns Of Bridge

The flow around a circular cylinder is a very common phenomenon both in our daily life and in real practice.With the rapid development of the society,China has built a large number of bridges and offshore structures,which play an important role both in economics and in daily life.The drag force and life force,with periodic changing oscillation which caused vortex shedding,may cause fatigue failure or even collapse.Once the damage occurs,it will cause huge economic losses.Therefore,precise estimation of drag force and lift force on bridge piers,as well as comprehensive understanding of the force generation mechanism,is of great significance for the real practice.The flow around a circular cylinder has been widely studied by researchers at home and abroad,and a series of useful results have been obtained.However,due to the limitations of experimental conditions and expensive costs,physical experiments are not frequently employed;numerical simulations are always aimed to 2D models as the 3D models requires lots of computing resources,which fails to truly simulate the surrounding of real bridge pier,whose submerged depth is small and the flow filed is three dimensional.In addition,the free surface is always ignored and one-phase flow is simulated,although the free surface may intensively influence the drag force and life force.Based on above disadvantages,this study aims to investigate the flow around isolated single column,twin columns and three columns arranged in different manners(i.e.tandem,side by side and staggered)by building 3D and two-phase flow model in ANSYS Fluent.The characteristics of drag force,lift force and flow field,as well as the generation mechanism of the drag force and lift force,will be analyzed,in detail:(1)Comparisons with existing experimental and numerical simulation data,the rationality and correctness of calculation parameters in numerical model,such as mesh size,turbulence model,decoupling method of control equation,etc.are verified.Based on which,the numerical calculation method suitable for three-dimensional two-phase flow in sub-critical region is determined.(2)The three-dimensional two-phase flow around an isolated single cylinder with free surface is studied.The flow field structure and other flow parameters,such as the pressure distribution on cylinder surface changing along the water depth,and the characteristics of three-dimensional flow field,are analyzed.(3)The three-dimensional two-phase flow around two cylinders in side-by-side,tandem and staggered arrangements is studied.The force characteristics,water flow parameters and three-dimensional flow field of each column are analyzed elaborately in the case of L/D=2.Influence of column space(L/D=3,4 and 5)on cylinder force and water flow parameters is also investigated.(4)The three-dimensional two-phase flow around three cylinders in side-by-side,tandem and staggered arrangements is studied.The force characteristics,water flow parameters and three-dimensional flow field of each column are analyzed elaborately in the case of L/D=2.Influence of column space(L/D=3,4 and 5)on cylinder force and water flow parameters is also investigated.The main achievements of this study is: the changing rule of the pressure distribution on column surface along water depth;the characteristics of the drag force,lift force and flow field for the twin columns and three columns arranged in tandem,side by side and staggered manners,as well as the generation mechanism of drag force and lift force;the rules of drag force,lift force and Strouhal number changing with the relative center distance L/D.These results would be beneficial to the calculation of current force of bridge substructure and the development of the measures to protect bridge from water hazard.