| With transportat ion demand increasing, long-span bridges achieve large development. Bridges have beco me flexible systems which are sensit ive to wind load. Hard flutter is a wind-induced self-excited vibrat ion which is easy to cause structural damage. Soft flutter has no obvious wind crit ical point, and characterized by continuous vibration. Therefore, it is meaningful to study flutte r and soft flutter and their flow contro l method to improve the level of wind resistant design o f long-span bridges.In this paper, hard flutter and so ft flutter of streamlined deck cross sect io n are studied by CFD numerical simulation. Moreover, new metho d o f flow contro l with the purpose of suppressing flutter will be proposed. The main research contents are as follows:Numerical calculat ion model of Sutong Bridge and Taohuayu Yellow River Bridge under constructing state are built. Using FLUENT, different scale model, mesh number, calculating t ime step and wind speed is considered in order to co mpare aerodynamic coefficients and properties o f flow field between the result of numerical calculat ion and wind tunnel test. The most opt imal parameters are selected for following study o f wind-induced vibrat ion.The crit ical flutter wind speed of two bridges at different attack angles are calculated by both forced vibrat ion method and direct calculation method. User defined funct ion(UDF)and dynamic mesh technology in FLUENT are used in direct calculation, which could realize simulation for the coupling o f wind and bridge decks. Structure vibration response of time-history curve at different attack angle and different wind speed are acquired by fourth order Runge-Kutta method. Then flutter crit ical wind at different working condit ions is achieved. At the same time, direct calculat ion method can search the range o f wind speed which can cause so ft flutter at certain attack angles. The vortex shedding mode at tail flow o f the bridge deck under different states is studied. Then, the relat ionship between the vortex and the response is explained.The flutter characterist ics o f the bridge under different attack angles are suppressed by a contro l plate which combined act ive and passive suction/jet flow contro l. For non-negat ive wind attack angle s, different distance between contro l plate and the bottom of bridge deck is analyzed. Then, the most optimized distance is picked. Act ive suction/jet flow contro l is used to contr o l the attack angles at which passive suct ion/jet method doesn ’t have effect. Meanwhile, different flow rate under certain flow rate for restraining flutter characteristics is considered. Finally, the contro l mechanism of the method is revealed by the contour of the velocit y flow line and vort ex contour in the flow filed. |
