On Simulation Of Turbulent Flow Around Bridge And Identification For System Characteristics

Based on Natunal Science Foundation of China(No:50978095), this paper focuses on simulation of turbulent flow around bridge and identification for system characteristics. The main studies are presented as follows:1) Turbulence models commonly used for engineering practice are introduced systematically,with the limitation and requirements (including grid,Yplus value) also presented.This help to provide good suggestions for turbulent simulation in bridge wind engineering.2) The characteristics and computational requirements of both the standard k -εturbulence model and the Shear-Stress Transports k -ωturbulence model are presented respectively in this paper. Then,the two models are employed to identify flutter derivatives of a real bridge deck.It is found that,based on suitable computational domain and grids arrangement, these models can identify most flutter derivatives of bridge decks with good accuracy. The discrepancy between specific flutter derivatives indicates that the SST k -ωturbulence model is more suitable to identify flutter derivatives of bridges.3) The turbulent flow around the fixed rectangular section B/D = 4 is simulated with FLUENT software. Then the pressure distribution on the cross section is analyzed by Principal Component Analysis(PCA). It is found that the first principal component shows a good agreement with RMS of fluctuating pressure distribution.Based on the shape of the first principal component, the average location of vortex shedding of the separation shear flow can be determined; Based on the first principal coordinate, the frequency of vortex shedding around a rectangular cross-section can be also determined. The main vortex shedding dominates the surface pressure fluctuation characteristics of the upper and lower surface of rectangular cross-section. This paper also conducts related research of Reynolds number effect on the principal components,which will help to study Reynolds number effect on flow around bridge decks.4) For forced vibration of the bridge section with varying amplitude, the flow field is simulated with FLUENT software, and the first principal component are analysed and compared. It is found that,the fluctuant intensity of pressure on the windward side of section is greater than other regions.Then the nonlinear between the pressure distribution and vibration amplitude is existent, which may be a factor causes the nonlinear of aerodynamic forces.5) Based on the theory of Volterra series and the method of the computational fluids dynamics (CFD),the first-order kernel of nonlinear aerodynamic force systems of the flat plate is identified,then the discrete-time aerodynamic models are established which can represent the unsteady aerodynamic behaviors of the flat plate. It is found that,for imposed displacement with a single frequency or broad-spectrum, the aerodynamic response can be otained quickly by these models.The nonlinear aerodynamic model established by the first order Volterra kernel is not enough to identify nonlinear aerodynamic forces and capture the nonlinear characteristics of flat ,but the work is a good try to identify nonlinear aerodynamic forces and research nonlinear characteristics of bridge decks.