Application of Snapshot POD Analysis in Extracting Flow Structures around Bridge Decks

The long span bridges have been much more flexible and vulnerable to wind induced vibrations due to their continuing increase of span length. To understand the mechanism of wind induced vibrations and achieve better vibration mitigation methods, the complex flow around the bridge decks have been carefully studied using advanced numerical simulations or advanced experimental techniques. In the present paper, the snapshot proper orthogonal decomposition (SSPOD) is used to analyze flow structures obtained from numerical simulations and fluid visualization techniques. The results from numerical simulations based on computational fluid dynamics (CFD) are compared with those from numerical simulations and experiments in the literature and Particle Image Velocimetry (PIV) experiments in the present study. For a demonstration purpose, flow structures around a square cylinder and a twin box bridge deck section were analyzed using the SSPOD. Periodical flow patterns were found in the downstream of the bluff body sections. The revised frozen turbulence hypothesis is used in the present study to analyze the vortex evolution in four phase angles when taking the lift coefficient as a reference signal. Vortex structures are successfully extracted and the vortices are found moving at a constant speed, while the non-dimensional frequency of the vortex moving is the same as the Strouhal number. For the twin-box girders, periodical flow pattern changes are found in the downstream of the twin-box girders, as well.