Active blowing flow control for VIV of streamlined box girder and its mechanism

In order to analysis the effect of flow vibration suppression measures based on active blowing on the vortex-induced vibration (VIV) performance of a streamlined box girder, a free-hanging wind tunnel test with a 1∶50 rigid segmental model was carried out, and the segmental model was connected to a blowing device to achieve the flow control effect. The VIV response of the girder at the most unfavorable attack angle of 5° was analyzed under different air hole parameters. The vertical VIV of the girder was reproduced through the numerical simulation, and the mechanism of active blowing in suppressing the VIV of the girder was analyzed. Research results show that obvious vertical and torsional VIV is observed in the original design section with an angle of attack of 5°. Specifically, two locking intervals are possessed by the vertical and torsional VIV, respectively, and the VIV response peaks appear in the second locking interval of the vertical VIV and the first locking interval of the torsional VIV. The VIV response amplitude and VIV interval of the girder are greatly affected by the active blowing flow control. The vertical VIV of the girder disappears when the blowing rate in the upstream and downstream or the downstream of a lower web is 10 m·s^-1, and the best suppression effect reaches 91.9%. The blowing rate of 5 m·s^-1 can obviously suppress the torsional VIV, and the best suppression effect of the torsional VIV reaches 65.4%. The VIV performance is significantly affected by the blowing rate. The vertical suppression effect at a blowing rate of 10 m·s^-1 is better than that at a blowing rate of 5 m·s^-1, while the torsional suppression effect at a blowing rate of 5 m·s^-1 is better than that at a blowing rate of 10 m·s^-1. The overall VIV control effect under a working condition with an air hole spacing of 2.5 m is better than that under a working condition with an air hole spacing of 5.0 m. The suppression effect under the working condition with air holes arranged on the lower web is better than that under the working condition with air holes arranged on the upper web. When the air holes are arranged on the downstream lower web, the blowing rate reaches 10 m·s^-1, and the air hole spacing is 2.5 m. The active blowing can reduce the periodic pulsing pressure difference on the downstream upper and lower surfaces of the girder and destroy the negative pressure center at the downstream lower web. Therefore, it can effectively suppress the vertical VIV of the girder. 2 tabs, 13 figs, 26 refs.