Abstract

Slender structures with circular cylindrical cross-sections are very common in civil engineering, industrial equipment and bridge engineering. Such long cylinders subjected to wind are columns, piles, long cables, chimney, pylons and others. On long cables, an instability called dry galloping has been recently theorized to be linked to an unpredictable jump state occurring once the boundary layers of the circular cylinder changes from laminar to turbulent. With a non-stationary character, the force generated at the critical flow regime is named bi-stable activity. In this work, the birth of bi-stable flow activity around a circular cylinder made of high-density polyethylene is studied experimentally in a wind tunnel. The pressure pattern is linearly decomposed and geometric modes governing the bi-stable activity as a function of circularity defect are created. The results show that the energy of the non-stationary load observed at the critical flow regime depends strongly on the circularity defect. Furthermore, the inclination angle of 60° confers a significant increase in the energy of the bi-stable flow mode when an unsteady asymmetric reattachment event occurs. The paper also highlights the variability of the mean drag coefficient as a function of the macroscopic defect.

摘要

具有圆柱横截面的细长结构在土木工程、工业设备和桥梁工程中非常常见。这种受风影响的长圆柱是柱子、桩、长电缆、烟囱、塔架等。在长电缆上，一种称为干驰骋的不稳定性最近被认为与一旦圆柱体的边界层从层流变为湍流时发生的不可预测的跳跃状态有关。由于具有非平稳特性，在临界流动状态下产生的力称为双稳态活动。在这项工作中，在风洞中对高密度聚乙烯制成的圆柱体周围双稳态流动活动的产生进行了实验研究。压力模式被线性分解，并创建了控制双稳态活动的几何模式作为圆度缺陷的函数。结果表明，在临界流动状态下观察到的非平稳载荷的能量很大程度上取决于圆度缺陷。此外，当发生非稳态不对称重新附着事件时，60° 的倾角使双稳态流动模式的能量显着增加。该论文还强调了作为宏观缺陷函数的平均阻力系数的可变性。当发生非定常不对称重新附着事件时，60°的倾角使双稳态流动模式的能量显着增加。该论文还强调了作为宏观缺陷函数的平均阻力系数的可变性。当发生非定常不对称重新附着事件时，60°的倾角使双稳态流动模式的能量显着增加。该论文还强调了作为宏观缺陷函数的平均阻力系数的可变性。