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Wind and Structures
  Volume 30, Number 4, April 2020, pages 367-378

Numerical study of wake and aerodynamic forces on a twin-box bridge deck with different gap ratios
Jingmiao Shang, Qiang Zhou, Haili Liao, Allan Larsen, Jin Wang and Mingshui Li

    Two-dimensional Delayed Detached Eddy Simulation (DDES) was carried out to investigate the uniform flow over a twin-box bridge deck (TBBD) with various gap ratios of L/C=5.1%, 12.8%, 25.6%, 38.5%, 73.3% and 108.2% (L: the gap-width between two girders, C: the chord length of a single girder) at Reynolds number, Re=4x104. The aerodynamic coefficients of the prototype deck with gap ratio of 73.3% obtained from the present simulation were compared with the previous experimental and numerical data for different attack angles to validate the present numerical method. Particular attention is devoted to the fluctuating pressure distribution and forces, shear layer reattachment position, wake velocity and flow pattern in order to understand the effects of gap ratio on dynamic flow interaction with the twin-box bridge deck. The flow structure is sensitive to the gap, thus a change in L/C thus leads to single-side shedding regime at L/C󖼩.6%, and co-shedding regime at L/C󖼳.8% distinguished by drastic changes in flow structure and vortex shedding. The gap-ratio-dependent Strouhal number gradually increases from 0.12 to 0.27, though the domain frequencies of vortices shedding from two girders are identical. The mean and fluctuating pressure distributions is significantly influenced by the flow pattern, and thus the fluctuating lift force on two girders increases or decreases with increasing of L/C in the single-side shedding and co-shedding regime, respectively. In addition, the flow mechanisms for the variation in aerodynamic performance with respect to gap ratios are discussed in detail.
Key Words
    twin-box bridge deck; Delayed Detached Eddy Simulation; vortex shedding; aerodynamic forces; gap ratios
Jingmiao Shang, Qiang Zhou, Jin Wang, Mingshui Li: Research Center for Wind Engineering, Southwest Jiaotong University, China
Allan Larsen: COWI Consulting Engineers and Planners A/S, Denmark

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