表面损伤斜拉索雷诺数临界区气动力与流场分析

Analysis of Aerodynamic and Flow Fields in Critical Reynolds Number Regime of Stay Cables with Surface Damage

斜拉索由于具有自身质量轻、结构刚度差、结构阻尼小和自身长细比大的特点,极容易发生风(雨)致振动,对桥梁结构的安全性能产生很大的影响,而斜拉索作为斜拉桥的重要受力构件,准确掌握其风荷载对于桥梁抗风设计具有重要意义,特别是斜拉索在生产、运输和安装过程中表面可能受到损伤,该斜拉索在临界雷诺数区的气动力特性和流场特性更是值得研究的问题。针对此种状况,通过同步测力风洞试验,对表面无损伤斜拉索模型和表面损伤斜拉索模型在不同风攻角下的升力系数进行时程分析,得到边界层转捩的3个区域;将升力系数时程进行快速傅里叶变换计算得到升力时程频谱图,并通过频谱图分析随机信号的频域特征;对比从雷诺数亚临界、临界到超临界区表面无损伤和表面损伤斜拉索的流场变化,并从周围流场变化的角度分析雷诺数临界区斜拉索气动稳定性及可能的机理。研究结果表明:表面无损伤和表面损伤模型的升力系数随雷诺数的变化规律基本一致,二者的升力时程在TrBL0向TrBL1阶段和TrBL1向TrBL2阶段过渡过程中会出现双稳态现象,损伤会影响斜拉索尾流区旋涡脱落的情况,进而对不同雷诺数下的Strouhal数值变化产生一定的影响。

Because of their characteristics of low weight, low structural stiffness, low structural damping, and large slenderness ratio, bridge cables are extremely susceptible to wind-and rain-induced vibrations, which have a considerable impact on the safety performance of a bridge structure. Because cables are essential members of a cable-stayed bridge, comprehensive understanding of the wind load on a cable-stayed bridge is critical. A cable may be damaged during production, transportation, or installation. Therefore, the aerodynamic and flow-field characteristics of a damaged cable in the critical Reynolds number regime are worthy of study. In this work, to study the aerodynamic and flow-field characteristics of a damaged cable in the critical Reynolds number regime, a time history analysis of the lift coefficient of intact and damaged cable models under different wind attack angles was conducted, and three regions of the boundary layer transition were identified. The lift-coefficient time history was calculated by fast Fourier transform, and a lift time history spectrum chart was obtained. In addition, the frequency domain characteristics of a random signal were analyzed based on the frequency spectrum. The flow-field changes and a comparison of the intact and damaged cables from subcritical and critical to supercritical Reynolds number regimes were analyzed. The aerodynamic stability and possible mechanism of the critical Reynolds number regimes were analyzed from the angle of change of the surrounding flow-field. Results show that the lift coefficient of the intact and damaged cable models is basically consistent with the change law of the Reynolds number, and the lift time history of the two cable models presents a bistable phenomenon during the transition from TrBL0 to TrBL1 and from TrBL1 to TrBL2. In addition, cable damage affects the vortex shedding in the wake area of the cable and further influences the numerical variation of the Strouhal number at different Reynolds numbers.