Clarification of Generation Mechanism for Transient Fluid-induced Forces on Bluff Body due to Gusty Wind

本文研制了一种可再现侧风的实验装置，用于测量沿导轨运行的方棱镜的瞬态升力。暗示与卡门涡脱落有一定关系。还指出了确定每个力分量的困难。利用另一种可引起纵风速突然增大的风洞，测量了一个方形棱柱和一组5个圆柱的瞬态气动力。研究发现，两侧面分离气泡的不对称产生对方柱瞬态升力的机理有重要影响。并找到了5个圆柱周围复杂的流动模式来确定瞬态力。CFD模拟结果较好地再现了瞬态力，证明了瞬态力与卡门涡的关系。对理想龙卷风引起的阵风时程进行了模拟，讨论了列车在龙卷风经过附近时的安全评价问题。

An experimental setup which can reproduce lateral wind was newly manufactured and was used for the measurement of transient lift force on a square prism running along a guide rail. Some relationship to Karman vortex shedding was implied. The difficulty to identify each force component was also pointed out.Transient aerodynamic forces on a square prism and a group of 5 circular cylinders were measured by use of another existing wind tunnel which can also generate sudden increase of longitudinal wind velocity. It was found that the asymmetric generation of separation bubbles on both side surfaces was important for the mechanism of transient lift on a square prism. And the complex flow pattern around the 5 circular cylinders was found to determine the transient forces. The transient forces were well reproduced by CFD simulation which showed an evidence of relationship with Karman vortex. A simulation of time history of gusty wind due to an ideal tornado was conducted to discuss safety evaluation of a train wagon during tornado passage nearby.