流线型钢箱梁涡激振动机理与气动控制措施

Study on Mechanism and Aerodynamic Control Measures for Vortex-induced Vibration of a Streamlined-box Steel Girder

以某主跨390 m的独塔流线型钢箱梁斜拉桥为工程依托,采用风洞试验与计算流体动力学(Computational Fluid Dynamics, CFD)相结合的方法对流线型钢箱梁涡激振动机理与气动控制措施进行研究。首先,采用几何缩尺比为1∶30的主梁节段模型进行主梁涡振性能与气动控制措施优化研究;其次,采用CFD方法对主梁涡振响应进行流固耦合计算,将Newmark-β算法嵌入ANSYS Fluent用户自定义函数(User Defined Functions, UDFs)实现主梁结构振动响应求解,同时结合动网格技术实现主梁断面流固耦合分析;并根据判断条件来检索箱梁壁面上的网格单元,以获得主梁断面振动过程中的表面压力,然后结合主梁结构振动响应、表面压力以及流场特征等对主梁涡激振动机理进行分析。结果表明:该桥主梁原设计方案存在涡激共振现象,将梁底检修车轨道内移120 cm可有效抑制主梁涡振响应;主梁涡激振动响应的数值模拟结果与风洞试验结果吻合较好;检修车轨道内移120 cm后主要改变了箱梁下表面平均压力系数分布特性,且箱梁表面各测点脉动压力卓越频率不一致,有效减小了主梁涡激振动响应;流线型箱梁靠近迎风侧的“被动区域”对结构涡振响应贡献较小,背风侧“驱动区域”发生周期性旋涡脱落是影响流线型箱梁涡振的主要因素。

Based on a single-pylon streamlined steel box girder cable-stayed bridge with a main span of 390 m, the vortex-induced vibration(VIV) performance and aerodynamic control measures of streamlined steel box girder were studied using wind tunnel tests and computational fluid dynamics(CFD), respectively. First, wind tunnel tests of the bridge deck sectional model with a geometry scale of 1∶30 were conducted to investigate the VIV responses and aerodynamic control measures. Second, the CFD method was used to calculate the VIV response of the main deck, and the Newmark-β algorithm was embedded in the user-defined functions(UDFs) of ANSYS Fluent to solve the vibration responses of the main deck. Moreover, dynamic grid technology was applied to analyze the fluid-structure interactions of the main deck. According to the checked conditions, the grid elements on the surface of the main deck were retrieved to obtain the pressure of the oscillating main deck section. Finally, the VIV mechanism of the main deck was analyzed based on the vibration responses, surface pressure, and flow characteristics of the main deck. The results show that the original design of the main deck exhibits the phenomenon of VIV, which can be effectively suppressed by moving the inspection rails at the bottom of the main deck inward. The numerical results for the VIV response of the main deck are in good agreement with the wind tunnel test results. The average pressure distribution characteristics on the lower surface of the main deck are mainly affected by moving the inspection rails inward by 120 cm, and the dominant frequency of fluctuating pressures at different points on the surfaces of the main deck is not consistent with each other, which effectively suppressed the VIV responses of the main deck. Furthermore, it was found that the “passive area” of the streamlined box girder near the windward side has a lower contribution to the VIV response. However, the periodic vortex shedding in the “driving area” on the leeward side of the streamlined box girder s the main factor affecting the VIV response of the streamlined box girder.