Numerical Simulation And Analysis Of Flow Field Around The Tandem Cylinder Piers

Aqueduct is a common conveyance structure,flow field around piers of aqueduct is complicated by pier settings,the variation of flow filed,vortex shedding and pressure distribution around piers are very important to study on the load and water damage mechanism of piers and riverbed erosion.At present,due to limitation of experiment condition,it's very difficult to do experimental studies on intandem piers at high Reynolds number and the simulation about it is rare. Study on flow field around three pires in specific project is done in this paper.The main work is as follows:(1)Because current study on flow field around circular cylinder is focus on single and twin column,study on flow field around piers and relevant mechanism analysis is rare,a new method to better simulate flow field around piers will be seeked in this paper.By reading a mass of literature,LES method is selected.Firstly,LES method is used to simulate flow field around single cylinder,compared with experimental results,it shows that LES method is realized successfully,then it can be applied to two-dimensional simulation of flow field around piers.(2)Two dimentional computational model of flow around piers is built,then the mesh refinement around piers is done and LES method is used to caculate flow field around piers on intandem piers at high Reynolds number.The velocity, pressure distribution and vorticity field are obtained,meanwhile,lift coefficients,drag coefficients,Strouhal numbers and frequencies of vortex shedding.are also gained.(3)Three dimentional computational model of flow around piers is built,then the mesh refinement around piers is done.Because three dimentional sizes of the model are very large and LES method needs very fine grid,limitied by computer power,the 3D simulation applies Reynolds equation instead of LES method.The velocity, pressure distribution and vorticity field are obtained,meanwhile,bed stresses,lift coefficients.drag coefficients,Strouhal numbers and frequencies of vortex shedding.are also gained.(4)Compared the simulation results of 2D with 3D,we find that the stations of stagnation points and separation points are different in 2D simulation but similar in 3D simulation. Good vortex street can be obtained by 2D simulation,vortex field which obtained 3D simulation has the nature of randomness and three-dimension characteristics.Drag coefficients obtained by 3D simulation are all positive which is inconsistent with the conclusion of 2D simulation,but both can obtain the conclusion that steady-state drag coefficient of middle pier is minimum.Lift coefficient of each pier which obtained by 2D and 3D simulation is near zero in the fluctuations.Frequencies of vortex shedding which obtained by 2D and 3D simulation are all low and there is a dominant frequency for each pier.Strouhal numbers which obtained by 2D and 3D simulation are little different. The research results of this thesis will be important references to analyses and design of piers.