LES study on variation of flow pattern around a 4:1 rectangular cylinder and corresponding wind load during VIV

Abstract

Vortex-induced vibration (VIV) is one of the typical flow-induced large amplitude vibrations. In this study, large eddy simulation (LES) is carried out to investigate the whole VIV process of a rectangular cylinder with aspect ratio 4. The flow fields and wind loads for rigid and elastic models are examined and compared to clarify the crucial flow characteristics during VIV. Results show that the time-averaged reattachment point of separated shear layer moves towards upstream direction with the increase of response amplitude. The mean negative pressure is consequently increased near leading edge of side face. For dynamic flow and wind load, in initial branch, the reattachment point of the separated shear layer, corresponding to the instant of largest side face wind load, gradually moves towards downstream with the increase of response amplitude. Meanwhile, the fluctuating lift coefficient and span-wise wind load correlation increase accordingly. In upper branch, the separated shear layer temporally separates from the side face, which leads to a sharp reduction of fluctuating lift coefficient and span-wise wind load correlation. The response amplitude, however, does not change apparently. In desynchronization, the response amplitude starts to decrease, as the vibration can no longer capture the shedding frequency of shape-induced vortex. The characteristics of the motion-induced wind loads corresponding to different wind speeds are also discussed in this study.