低质量比舵系统流致振动特征研究

Flow induced vibration characteristics of a hydrofoil system with a low mass ratio

考虑到舵的展弦比对其振动特性可能造成影响,将经典两自由度系统动力方程进行参数修正。方程中代表惯性效应的项引入附加质量修正系数,而环量项引入环量修正系数,并通过MATLAB编程求解方程得到了不同来流速度时舵系统的时历曲线以及相轨线;随着来流速度的增加,相轨线的形状趋于扁平化,这意味着系统的动能可以转化为更大的势能;此外,利用有限体积法结合半隐式积分法对计算区域进行离散,并选择SIMPLE算法对离散后的控制方程进行求解,从而模拟了流体作用下舵系统的瞬态运动,分析了舵系统发生颤振时的绕流场变化。发现在舵的上表面,前缘和刚心之间的涡不断向后缘扩散,并在刚心和后缘之间形成了明显的涡层,此时舵的上表面形成一个完整的涡层,这与系统做衰减运动时有所不同;并且系统会出现大角度的俯仰运动,此时前缘和刚心之间出现较大的涡量。

Considering the potential impact of aspect ratio on the vibration of structures,the classical Theodorsen equation for the motions of two-degree-of-freedom foils was derived with the modification of its mass parameter and circulation parameter.The time-history curves and the phase orbits of the hydrofoil system at different values of inflow velocity were obtained by solving the equation through MATLAB programming.As the inflow velocity increases,the shape of phase orbits tends to be flattened,which means that the kinetic energy of the system can be transformed into a larger potential energy.Moreover,the finite volume method and semi-implicit integration method were used to discretize the computational domain,and the discrete governing equations were solved with the SIMPLE algorithm.Based on the results of numerical simulation,the transient motion of the hydrofoil system induced by fluid was solved,and the variation of the flow distribution around the hydrofoil during fluttering was analyzed.It is shown that the vortex between the leading edge and the elastic axis on the upper surface gradually spreads towards the trailing edge,forming a vorticity layer.The vorticity layer covers the whole upper surface of the hydrofoil,which is different from attenuated vibrations.As the hydrofoil pitches up,new vorticity layers are generated near the leading edge,and meanwhile the vorticity layer at the trailing edge moves downstream,forming a starting vortex nearby.