The Research On Aerodynamic Interference Effect On Two Decks In Tandem For Large-span Bridges Based On FLUENT

In order to increase the traffic capacity of bridges, the bridges tend to be designed as ones with double decks or twin decks displayed in tandem. In this paper, the study mainly aims at the research of the aerodynamic interference effect on the latter ones. In engineering practice, there are mainly two categories of twin bridges: 1)The twin bridges with decks designed to be two separate parallel ones when the bridges are both newly built; 2)The twin bridges formed due to the newly built one is constructed next to the older one and parallel to it after several years. The windward and leeward decks of these two kinds of bridges effect each other as a result of the short distance between themselves under wind load, such as the problems of vortex-induced vibration, stability of flutter, buffeting of twin bridges generated due to the aerodynamic interference effect on the windward deck and leeward deck and the difference of wind load between the windward deck, leeward deck and a single one. All these effects are so-called "aerodynamic interference effects". Aerodynamic interference effect on twin bridges can not be neglected with the increasing of the span, and becomes one of the most concerned problems.The research of aerodynamic interference effect on two decks displayed in tandem supported by National Science Foundation of China(No.50608030)in this paper conducts numerical simulation analysis for the aerodynamic interference effect on large-span twin bridges by means of the FLUENT, a large fluid calculation software, and lays emphasis on the law of aerostatic coefficients of three component forces varying with the distance between the bridges and aerodynamic interference effect on vortex-induced vibration of the two decks displayed in tandem. The main contents of research are as follows:(1)Firstly, utilizing k-ωSST turbulence model, a numerical simulation of single stationary square cylinder was conducted then compared with the wind tunnel experiment results in order to check the precision of the numerical simulation method adopted in this paper; Secondly, following the first step, a numerical simulation of single∏-shaped section and streamlined section was conducted and predicted the aerostatic coefficients of three component forces and Strouhal Number of them; Finally, interference factor was introduced and the distance between the two cross sections were changed for the three typical sections, namely, square sections,∏-shaped sections and streamlined sections, hoping to find the law of aerodynamic interference effect on the aerostatic coefficients of windward and leeward section with the change of distance between them.(2) Navier-Stokes equations of impressible viscid flow were solved using k-co SST turbulence model in FLUENT software. The initial mesh was built by adopting the domain decomposition method, "rigid moving zone plus dynamic zone plus stationary zone", and the dynamic response of the structure was solved by the dynamic mesh and embedding the code of Newmark-βmethod in user defined functions of FLUENT.In this way, the method of numerical simulation for the vortex-induced vibration of bluff structure was established. After that, this method was applied to simulate vortex-induced vibration of two different square cylinders with different ratio of width to height (B/H),4 and 5, in varied cases with different wind velocity. The results of numerical simulation agreed well with the wind tunnel experiment results.(3) Using the method of numerical simulation for the vortex-induced vibration of bluff structure adopted in chapter 4, aerodynamic interference effect on the vortex-induced vibration of two rectangular cylinders displayed in tandem under different ratio of net distance to width(D/B),0.5 and 1.0, was numerically simulated, followed by the comparison with the results of wind tunnel experiments. Generally speaking, the wind speed leading to the vortex-induced vibration slightly increases. The vibration amplitudes of two sections displayed in tandem go up notably, however, due to the aerodynamic interference effect within a short distance. This result agrees well with the experiment result, indicating that aerodynamic interference effect of two sections displayed in tandem can not be neglected when the ratio of distance to width is small.(4) In the chapter of conclusion and prospect, this paper briefly summarizes achievement, clarifies the deficiencies of the study and makes recommendations for the emphasis of the coming research.