箱梁颤振过程中旋涡的演化规律及气动力的变化特性

利用粒子图像测速技术（PIV）观测了箱梁颤振过程中模型周围流场的旋涡特征，以模型扭转振动位移作为参考信号，采用相位平均的方法研究了旋涡规律性演化对模型周期性振动的驱动作用。风速较低时，箱梁振幅很小，其尾部风嘴附近上侧的旋涡尺度也很小，不易观测到，而下侧的旋涡尺度较大，其形状接近于圆形。当风速接近颤振临界风速时，箱梁振幅明显增大，并且模型尾部风嘴上侧的旋涡尺度也显著增大，达到与下侧旋涡尺度相匹配的程度，模型尾部风嘴上下侧旋涡的交替作用主导了结构振动直到模型振动发散。基于流固松耦合的计算策略，采用计算流体动力学（CFD）的数值方法模拟了箱梁颤振临界状态下的绕流特性，结合正交特征分解（POD）的方法研究了模型颤振时刻表面压力的空间分布特征，通过分析发现在颤振过程中箱梁表面波动压力的主控成分向迎风侧风嘴漂移。

The vortex evolution and aerodynamic variation characteristic of box girders during the flutter

The characteristics of vortexes in the flow field around the model were observed by the particle image velocimetry （PIV） techniques during the box girder fluttered. Taking the mod- el torsional vibration displacement as a reference signal, the effect of the vortex regularity evolu- tion on the model periodic vibration was researched by the phase-average method. When the wind speed was low, the amplitude of structure was small. At the same time, the upside vortex near the rear nozzle was very small and not easily observed, but the downside vortex scale was larger, and its shape was close to a circle. While the wind speed was close to the critical flutter wind speed, the structure amplitude suddenly increased, and the scale of the upside vortex near the rear wind lips also significantly increased, achieving to the downside vortex scale. The effect of alternating vortex near the rear wind lips led to the vibration of model until the structural diver- gence. The flow characteristics around the box girder in the flutter were simulated by using com- putational fluid dynamics （CFD） numerical method based on the loosely coupled method. The space distribution features of surface pressure on the model in the flutter were analyzed by the proper orthogonal decomposition （POD） technique. The research shows that the main component of fluctuation pressure drifts to windward side of the nozzle.