飞行器自激振荡的流动物理与动力学机制

全局亚迭代耦合求解流体动力学方程和刚体动力学方程,研究轴对称飞行器单自由度俯仰失稳运动的非定常特征.高超音速锥-柱-裙飞行器的单自由度俯仰失稳运动发展为极限环形式,周期性运动伴随着波系结构的非定常变化;自激振荡源于静稳定构型的振动回复机制和尾裙激波流动迟滞效应所构成的阻尼机制.基于第二拉格朗日方程和虚功原理,导出能够描述迟滞现象的参数化非线性动力学模型.多尺度近似分析获得参数化运动特征:自激振动过程是拟简谐运动;静稳定构型才能出现自激振荡周期运动;平衡点阻尼是决定运动稳定特性的分叉参数;振幅特性与阻尼非线性相关,频率特性与刚度非线性相关.基于数值结果的参数辨识,非线性模型的理论分析、重构都与数值结果高度一致,从而有效地佐证了自激振荡建模研究的合理性.

Flow physics and dynamics mechanism of self-oscillation of an flight vehicle

A coupling numerical method, synchronously solving the coupled fluid dynamic equations and rigid dynamic equations with the global sub - iteration technique, is proposed to investigation the self - excited unsteady pitching motion of a hypersonic axial - symmetric configuration. The numerical results show that the unstable free pitching of the flared axial - symmetric vehicle develops into the limit - cycle motion with the periodical variation of the unsteady flow structure. The self - oscillation is caused by the restoring mechanism of the static - stable configure and the damping mechanism resulting from the flow hysteresis of shock wave at the skirt section. The nonlinear dynamic equation, which can characterize the hysteresis, is deduced basing on the second Lagrange equation and principle of virtual work. The parameterized motion is analyzed approximately by MTS method. The self- oscillation is the quasi simple harmonic motion and the static stability of the aircraft is necessary for such periodical motion. The damping at the equilibrium point is a bifurcation parameter determining the dynamic stability. The amplitude is correlated with the nonlinear damping and the frequency is correlated with the nonlinear rigidity. The theoretical analysis and the numerical reconstruction about such nonlinear model embodied by parameter identification agree well with the CFD results, validating the modeling method.