考虑振动频率及振幅变化影响的桥梁断面气动特征分析

Analysis of aerodynamic characteristics of bridge section with varied oscillating frequency and amplitude

为探究不同振动频率、振幅对桥梁断面气动特性的影响,利用可在静止网格中计算动边界绕流问题的浸入边界算法,编写出数值计算程序,展开竖向正弦强迫振动桥梁断面的绕流模拟,其振幅变化范围A=0.14 D^0.25 D,振动频率变化范围Stc=0.1~0.25。研究发现:不同振幅下的桥梁断面阻力系数均在静止涡脱频率处产生峰值,桥梁断面升力系数则在此处均出现归零效应,且振幅越大,归零效应愈明显;迎风面下翼缘可能是决定桥梁断面阻力系数和升力系数随振动频率变化的关键因素,桥梁结构在不同振动频率处呈现不同的涡量分布,但是在同一振动频率处仅改变物体运动振幅,断面流场涡量分布基本保持不变;振动频率是决定表面脉动压力分布的重要因素,振幅只会改变其值的大小,不影响其脉动压力分布特性。

In order to investigate the influence of oscillating frequency and amplitude variation on the aerodynamic characteristics of bridge section,the immersed boundary method,which can compute the moving boundary on the stable grid,is adopted in this paper to compile numerical calculation program.Then the simulation of flow around forced oscillating bridge section in transverse sinusoidal mode is carried out,in which the range of oscillating amplitude(A)is varied from 0.14 D to 0.25 D and frequency St c is from 0.1 to 0.25.The results indicate that mean drag coefficients of the oscillating bridge section with different oscillating amplitudes all reach the max value near the stable vortex shedding.Whereas mean lift coefficients of the oscillating bridge section all back to zero at this point.The lower surface of windward may be viewed as a critical factor to determine the mean drag and lift coefficient of the bridge section.Vortex contours of the bridge section appear differences at varying oscillating frequency,while vortex contours of bridge section retain constant at different oscillating amplitudes with the same frequency.Oscillating frequency is the crucial factor to determine the fluctuating pressure distribution on surface.Oscillating amplitude only change the magnitude of fluctuating pressure,not its distribution characteristics.