双自由度D形截面柱体流致振动的二维数值模拟

Two-dimensional numerical simulation of two-degree-of-freedom flow-induced vibration of D-section prism

本文研究了D形截面柱体在顺流向和横流向两个自由度下的流致振动特性,迎流角为90°,质量比为2.6,雷诺数为370~3685,应用RANS方程采用SST k-ω湍流模型和Newmark-β法求解水流运动和柱体运动,入口流速采用匀加速法,检验了数值模型的网格和时间步长敏感性,并与相关文献的实验结果进行对比,验证了数值模型的可靠性。基于计算结果,系统分析了D形截面柱体的振幅、振动频率、水动力系数、尾涡脱落模式,以及平均位置偏移情况。结果表明,双自由度D形截面柱体在约化速度为8~14的区间内表现为涡激振动-驰振模式,尾涡多为2S和S+2S交替脱落,双自由度振幅比单自由度有显著的增大。升力主要偏向截面的直线边一侧,且升力出现了多个倍频。横流向和顺流向平均偏移量最大都可达到一倍特征长度以上。

Two-dimensional numerical simulation was conducted to investigate the characteristics of fluid-induced vibration of a D-section prism with two degrees of freedom at an attack angle of 90°and a mass ratio of 2.6.The RANS equations were solved with the SST k-ωturbulent model closure.Uniform acceleration of inlet velocity and Newmark-βmethod were incorporated.Firstly the sensitivity analysis of the grid and time step in the present numerical model was carried out,then the comparisons with published experimental re-sults were made to validate the existing numerical model.Then,a systematic analysis of response amplitude,vibration frequency,hydrodynamic coefficient,wake vortex shedding mode and average position-offset was made.The D-section prism exhibits combined response of VIV and galloping modes at a reduced velocity range of Ur=8-14,with vortex shedding pattern alternating between 2S and S+2S.The response amplitude of the two-degree-of-freedom prism is often stronger than that of the one-degree-of-freedom one.The lift force is inclined to the straight side of the section,and more than one frequency multiplications were found for the lift force.The average position-offsets of both cross-flow and downstream direction have maximum values exceeding one characteristic length.