流线闭口箱梁涡振气动力的雷诺数效应研究

Reynolds number effects on aerodynamic forces of a streamlined closed-box girder during vortex-induced vibrations

涡激振动是大跨度桥梁在低风速易发的自限幅风致振动现象。针对典型流线闭口箱梁断面,分别进行了1∶70和1∶20主梁节段模型同步测振、测压风洞试验,对应以梁高为特征尺寸雷诺数范围分别为6.08×10^3~2.28×10^4和1.06×10^4~1.40×10^5,研究了雷诺数效应对箱梁涡振响应及表面气动力时频特性的影响。+3°初始攻角下,主梁断面存在明显涡振现象。与小比尺模型相比,大比尺模型竖向涡振发生风速低,振幅大,且出现了小比尺模型未观测到的扭转涡振现象。分别选取典型风速结点,进行表面气动力时频特性分析表明:不同雷诺数条件下,表面平均风压系数、压力系数根方差及分布气动力与涡激力相位差空间分布均有所不同,表现出显著的雷诺数效应;高雷诺数时,上表面下游、中上游和下表面区域气动力对涡激力贡献较大,其中上表面下游区域气动力对涡激力起增强作用,其它区域气动力对涡激力起抑制作用;低雷诺数时,上表面中上游区域气动力对涡激力几乎无贡献,上表面下游区域气动力对涡激力的贡献与高雷诺数时相近,下表面区域和迎风面斜腹板区域气动力对涡激力抑制作用远小于高雷诺数时。特别是下表面与下游风嘴转角附近区域气动力对涡激力抑制作用远大于高雷诺数时,可推断这正是低雷诺数时涡振幅值远小于高雷诺数时的主要原因。

Aiming at a traditional streamlined closed-box girder of long-span bridges,wind tunnel tests of synchronal measurement of pressures and displacement responses of a spring-suspended sectional model with scales of 1∶70 and 1∶20 were conducted,with Reynolds number of 6.08×10^3-2.28×10^4 and 1.06×10^4-1.40×10^5 respectively,and then effects of Reynolds number on wind-induced vibration(VIV)as well as time-frequency characteristics of the aerodynamic forces on the surface of the girder were revealed.It was found that there were obvious VIV phenomena both at low and high Reynolds number.Compared with VIV performance at low Reynolds number,lock-in regions were lower and maximum amplitudes were smaller at high Reynolds number,indicating that VIV performance at low Reynolds number was more unfavorable.Then time-frequency characteristics of the aerodynamic forces were investigated.It was found that the spatial distribution characteristics of mean pressure coefficients,RMS of pressure coefficients and phase lags between vortex-excited forces(VEF)and distributed aerodynamic forces were obviously different at different Reynolds numbers,which indicated that there were significant Reynolds number effects.The distributed aerodynamic forces in downstream and middle-upper reaches of the upper surface,as well as the lower surface contributed mostly to the VEF at high Reynolds number.The aerodynamic forces in downstream of the upper surface as well as lower surface had enhancement effects on the VEFs,while those in other regions had suppression effects on the VEFs.However,aerodynamic forces in middle-upper of the upper surface contributed little to the VEFs at low Reynolds number,and the contribution of aerodynamic forces in the downstream of the upper surface were very close to that at high Reynolds number.The negative contribution of aerodynamic forces to VEF in lower surface and windward inclined web were far smaller at low Reynolds number than that at high Reynolds number,while that in corner region of lower surface and tail wind fairing were far higher at low Reynolds number than that at high Reynolds number,which was responsible for the fact that VIV responses at high Reynolds number were higher than that at low Reynolds number.